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Rationale & Objective: Low muscle mass is common among older adults and associated with poor prognosis. Quantifying muscle mass is challenging in routine clinical practice. We hypothesized that glomerular filtration of creatinine (GF cr ) reflects muscle mass, and previously proposed estimated GF cr (eGF cr ), as a practical index of muscle mass in older adults. This study investigated whether measured GF cr (mGF cr ) and eGF cr are similarly associated with the direct measure of muscle mass, the thigh total muscle lean area (TTMLA)., Study Design: Cross-sectional analysis of a community-based prospective cohort., Setting & Participants: A total of 794 older adults with measured glomerular filtration rate (mGFR) and TTMLA in the AGES-Reykjavik Study., Exposure: Measured GF cr , the product of serum creatinine (Scr) and mGFR obtained using plasma iohexol clearance and eGF cr , the product of Scr and estimated glomerular filtration rate using serum cystatin C (Scys)., Outcome: TTMLA measured using computed tomography., Analytical Approach: Sex-specific Pearson's correlation and linear regression analyses using continuous and categorical mGF cr and eGF cr . Covariates included demographic, behavioral, and clinical variables, and comorbid conditions., Results: The mean age and mGFR were 80.3±4.0 (SD) years and 62.3±16.5 (SD) mL/min/1.73m 2 , respectively. The lowest sex-specific tertile of mGF cr , compared with the highest tertile, was associated with a 14.6 (95% CI, 11.5-17.6) cm 2 /1.73m 2 lower TTMLA in men, and a 7.9 (95% CI, 5.5-10.2) cm 2 /1.73m 2 lower TTMLA in women. Significant associations were observed between eGF cr and TTMLA. Correlations of eGF cr with TTMLA were generally as strong or stronger than correlations of alternative indices derived from Scr and Scys., Limitations: Residual confounding by measured and unmeasured variables., Conclusions: These findings support the validity of GF cr as an index of muscle mass among older adults and the use of eGF cr as a practical alternative to mGF cr in the clinical setting., Plain-Language Summary: Low muscle mass is common among older adults and is associated with poor clinical outcomes. Quantifying muscle mass is challenging in routine clinical practice. We evaluated whether glomerular filtration of creatinine (GF cr ) could serve as an index of muscle mass. We performed a cross-sectional study including 794 older adults who underwent computed tomography for thigh muscle lean area as a directly measured indicator of total body muscle mass. Significant positive associations between thigh muscle lean area and both measured GF cr (serum creatinine [Scr] ×measured glomerular filtration rate [GFR]) and estimated GF cr (Scr ×estimated GFR based on serum cystatin C [Scys]), a more practical index, were shown. These findings suggest the value of using eGF cr , a simply obtained novel index in the clinical setting, to assess muscle mass among older adults., (Copyright © 2024 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)

Assessing glomerular filtration rate (GFR) is critical for diagnosis, staging, and management of kidney disease. However, accuracy of estimated GFR (eGFR) is limited by large errors (>30% error present in >10-50% of patients), adversely impacting patient care. Errors often result from variation across populations of non-GFR determinants affecting the filtration markers used to estimate GFR. We hypothesized that combining multiple filtration markers with non-overlapping non-GFR determinants into a panel GFR could improve eGFR accuracy, extending current recognition that adding cystatin C to serum creatinine improves accuracy. Non-GFR determinants of markers can affect the accuracy of eGFR in two ways: first, increased variability in the non-GFR determinants of some filtration markers among application populations compared to the development population may result in outlying values for those markers. Second, systematic differences in the non-GFR determinants of some markers between application and development populations can lead to biased estimates in the application populations. Here, we propose and evaluate methods for estimating GFR based on multiple markers in applications with potentially higher rates of outlying predictors than in development data. We apply transfer learning to address systematic differences between application and development populations. We evaluated a panel of 8 markers (5 metabolites and 3 low molecular weight proteins) in 3,554 participants from 9 studies. Results show that contamination in two strongly predictive markers can increase imprecision by more than two-fold, but outlier identification with robust estimation can restore precision nearly fully to uncontaminated data. Furthermore, transfer learning can yield similar results with even modest training set sample size. Combining both approaches addresses both sources of error in GFR estimates. Once the laboratory challenge of developing a validated targeted assay for additional metabolites is overcome, these methods can inform the use of a panel eGFR across diverse clinical settings, ensuring accuracy despite differing non-GFR determinants., Competing Interests: Dr. Inker reports research grants to institution from the National Institute of Health/National Institute of Diabetes and Digestive and Kidney Diseases (grant 1R01DK116790), National Kidney Foundation, Chinnocks, Omeros and Reata Pharmaceuticals; consulting fees from Diamtrix; and participation on the medical advisory council for Alport Foundation and the scientific advisory board for National Kidney Foundation. Dr. Levey reports research grants to institution from the National Institute of Diabetes and Digestive and Kidney Diseases and National Kidney Foundation; royalties from UpToDate; honoraria from academic medical centers for visiting Professorships or Lectures; payment from AstraZeneca for participation on data safety/advisory board for clinical trials of Dapagliflozin. Dr. Greene reports research grants from the National Kidney Foundation, Collaborative Study Group, National Institutes of Health, and Patient-Centered Outcomes Research Institute. Dr. Haaland reports NIH R01 grant ad consulting fees from the National Kidney Foundation. Dr. Coresh reports grants from the National Institutes of Health and being scientific advisor to healthy.io. Dr. Kalil reports receiving research grant from Eurofins. Dr. Shlipak reports grants to his institution from Bayer Pharmaceuticals and National Institutes of Health – National Institute of Aging, National Institute of Diabetes and Digestive and Kidney Diseases, and National Heart Lung and Blood Institute; consulting fees from Cricket Health; honorarium from Boehringer Ingelheim, Astra Zeneca, and Bayer pharmaceuticals; payment for expert testimony from Hagens Berman International law firm; and serving as Chairman board of directors of Northern California Institute for Research and Education. Consulting fees and payments from commercial companies provided support in the form of salaries for authors but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section. These commercial affiliations do not alter our adherence to PLOS ONE policies on sharing data and materials., (Copyright: © 2024 Fino et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Competing Interests: Disclosures: Disclosure forms are available with the article online.

Pharmacologic interventions to slow chronic kidney disease progression, such as ACE-inhibitors, angiotensin receptor blockers, or sodium glucose co-transporter 2 inhibitors, often produce acute treatment effects on glomerular filtration rate (GFR) that differ from their long-term chronic treatment effects. Observational studies assessing the implications of acute effects cannot distinguish acute effects from GFR changes unrelated to the treatment. Here, we performed meta-regression analysis of multiple trials to isolate acute effects to determine their long-term implications. In 64 randomized controlled trials (RCTs), enrolling 154,045 participants, we estimated acute effects as the mean between-group difference in GFR slope from baseline to three months, effects on chronic GFR slope (starting at three months after randomization), and effects on three composite kidney endpoints defined by kidney failure (GFR 15 ml/min/1.73m 2 or less, chronic dialysis, or kidney transplantation) or sustained GFR declines of 30%, 40% or 57% decline, respectively. We used Bayesian meta-regression to relate acute effects with treatment effects on chronic slope and the composite kidney endpoints. Overall, acute effects were not associated with treatment effects on chronic slope. Acute effects were associated with the treatment effects on composite kidney outcomes such that larger negative acute effects were associated with lesser beneficial effects on the composite kidney endpoints. Associations were stronger when the kidney composite endpoints were defined by smaller thresholds of GFR decline (30% or 40%). Results were similar in a subgroup of interventions with supposedly hemodynamic effects that acutely reduce GFR. For studies with GFR 60 mL/min/1.73m 2 or under, negative acute effects were associated with larger beneficial effects on chronic GFR slope. Thus, our data from a large and diverse set of RCTs suggests that acute effects of interventions may influence the treatment effect on clinical kidney outcomes., (Copyright © 2024 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Background: Black individuals are historically underrepresented in oncology clinical trials. One potential reason for this is the prevalence of kidney disease in Black individuals, utilization of estimated creatinine clearance as a surrogate for glomerular filtration rate (GFR) in oncology, and GFR-based trial eligibility criteria. We characterized the representation of racial minorities in anticancer agent pivotal trials and examined if GFR-based trial eligibility criteria impact the proportion of Black individuals in trial populations., Methods: We constructed a data repository for anticancer drugs FDA-approved from 2015 to 2019 and associated pivotal trials, from which we extracted trial population racial compositions and GFR-based trial eligibility criteria. We calculated the participation-to-incidence ratio (PIR) and participation-to-mortality ratio (PMR) for a variety of cancer sites, where PIR or PMR >1.2 and <0.8 indicate overrepresentation and underrepresentation, respectively. We evaluated the relationship between GFR eligibility cutoffs and the proportion of Black enrollees with Spearman rank correlation coefficient., Results: We assessed 24,698 patients in 74 trials. Black individuals were underrepresented in all trials (PIR ≤0.48, PMR ≤0.50). For trials with GFR-based eligibility criteria (n = 49), a lower GFR cutoff was modestly associated with a higher proportion of Black enrollees (r = -0.29, p = 0.039). This relationship was strengthened for trials that only used estimated creatinine clearance to estimate GFR (r = -0.43, p = 0.004)., Conclusions: GFR-related eligibility, and specifically the use of estimated creatinine clearance, may contribute to Black individuals being disproportionately excluded from cancer clinical trials. This highlights the need for implementation of contemporary GFR equations and other interventions to boost racial minority trial enrollment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Rationale & Objective: β 2 -Microglobulin (B2M) and β-trace protein (BTP) are novel endogenous filtration markers that may improve the accuracy of estimated glomerular filtration rate (eGFR) beyond creatinine and cystatin C (eGFR cr-cys ), but they have not been assessed in patients with cancer., Study Design: Cross-sectional analysis., Setting & Participants: Prospective cohort of 1,200 patients with active solid tumors recruited between April 2015 and September 2017., Exposure: CKD-EPI equations without race combining B2M and/or BTP with creatinine with or without cystatin C (2-, 3-, or 4-marker panel eGFR)., Outcome: Performance of equations compared with eGFR cr-cys and non-GFR determinants of serum B2M and BTP (S B2M , and S BTP , respectively). Measured GFR (mGFR) was determined using the plasma clearance of chromium-51 labeled ethylenediamine tetraacetic acid ( 51 Cr-EDTA)., Analytical Approach: Bias was defined as the median of the differences between mGFR and eGFR, and 1-P 30 was defined as the percentage of estimates that differed by more than 30% from the mGFR (1-P 30 ). Linear regression was used to assess association of clinical and laboratory variables with S B2M , and S BTP after adjustment for mGFR., Results: Mean age and mGFR were 58.8±13.2 SD years and 78.4±21.7 SD mL/min/1.73m 2 , respectively. Performance of the 3-marker and 4-marker panel equations was better than eGFR cr-cys (lesser bias and 1-P 30 ). Performance of 2-marker panel equations was as good as eGFR cr-cys (lesser bias and similar 1-P 30 ). S B2M and S BTP were not strongly influenced by cancer site., Limitations: Participants may have had better clinical performance status than the general population of patients with solid tumors., Conclusions: B2M and BTP can improve the accuracy of eGFR and may be useful as confirmatory tests in patients with solid tumors, either by inclusion in a multimarker panel equation with creatinine and cystatin C, or by substituting for cystatin C in combination with creatinine., Plain-Language Summary: The most accurate method to assess estimate kidney function is estimated glomerular filtration rate (eGFR) using creatinine and cystatin C (eGFR cr-cys ). We studied whether using β2-microglobulin (B2M) and/or β-trace protein (BTP) with creatinine with or without cystatin C (2-, 3-, or 4-marker panel eGFR) might be useful in patients with active solid tumors. The performance of the 3-marker and 4-marker panel equations was better than eGFR cr-cys . Performance of 2-marker panel equations was as good as eGFR cr-cys . We conclude that B2M and BTP can improve the accuracy of eGFR and may be useful as a confirmatory test in patients with solid tumors either by inclusion in multimarker panel equation with creatinine and cystatin C or by substituting for cystatin C in combination with creatinine., (Copyright © 2024 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)

Background: Patients with atrial fibrillation and severe chronic kidney disease have higher risks of bleeding, thromboembolism, and mortality. However, optimal anticoagulant choice in these high-risk patients remains unclear., Methods and Results: Using deidentified electronic health records from the Optum Labs Data Warehouse, adults with atrial fibrillation and severe chronic kidney disease (estimated glomerular filtration rate <30 mL/min per 1.73 m 2 ) initiating warfarin, apixaban, or rivaroxaban between 2011 and 2021 were included. Using inverse probability of treatment weighting, adjusted risks of major bleeding, stroke/systemic embolism, and death were compared among agents. A total of 6794 patients were included (mean age, 78.5 years; mean estimated glomerular filtration rate, 24.7 mL/min per 1.73 m 2 ; 51% women). Apixaban versus warfarin was associated with a lower risk of major bleeding (incidence rate, 1.5 versus 2.9 per 100 person-years; subdistribution hazard ratio [sub-HR], 0.53 [95% CI, 0.39-0.70]), and similar risks for stroke/systemic embolism (incidence rate, 1.9 versus 2.4 per 100 person-years; sub-HR, 0.80 [95% CI, 0.59-1.09]) and death (incidence rate, 4.6 versus 4.5 per 100 person-years; HR, 1.03 [95% CI, 0.82-1.29]). Rivaroxaban versus warfarin was associated with a higher risk of major bleeding (incidence rate, 4.9 versus 2.9 per 100 person-years; sub-HR, 1.65 [95% CI, 1.10-2.48]), with no difference in risks for stroke/systemic embolism and death. Apixaban versus rivaroxaban was associated with a lower risk of major bleeding (sub-HR, 0.53 [95% CI, 0.36-0.78])., Conclusions: These real-world findings are consistent with potential safety advantages of apixaban over warfarin and rivaroxaban for patients with atrial fibrillation and severe chronic kidney disease. Further randomized trials comparing individual oral anticoagulants are warranted.

Background: Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce heart failure (HF) hospitalizations, recurrent cardiovascular events, and chronic kidney disease (CKD) progression, and thus constitute a Class 1a recommendation in people with diabetes and atherosclerotic cardiovascular disease, HF, or CKD and in people with severe albuminuria or HF, regardless of diabetes status., Objectives: The purpose of this study was to comprehensibly characterize the rate of SGLT2 inhibitor prescriptions among people with a Class 1a recommendation for SGLT2 inhibitor use., Methods: Among 3,189,827 adults from 28 U.S. health systems within Optum Labs Data Warehouse between April 1, 2022, and March 31, 2023, we assessed SGLT2 inhibitor prescription rates, stratified by presence of diabetes and Class 1a recommendation., Results: Among 716,387 adults with diabetes, 63.4% had a Class 1a recommendation for SGLT2 inhibitor therapy. There was little difference by Class 1a recommendation status (present: 11.9%; 95% CI: 11.9%-12.0% vs absent: 11.4%; 95% CI: 11.3%-11.6%; standardized mean difference: 1.3%). Among 2,473,440 adults without diabetes, 6.2% had a Class 1a recommendation for SGLT2 inhibitor therapy, and 3.1% (3.0%-3.2%) of those received a prescription. Internists/family practitioners initiated SGLT2 inhibitor prescriptions most commonly among people with diabetes, whereas specialists initiated SGLT2 inhibitor prescriptions most commonly among people without diabetes. No health system had >25% SGLT2 inhibitor prescription rate among people with a Class 1a recommendation. Health systems with higher proportions of patients with commercial insurance and lower proportions with Medicare had higher SGLT2 inhibitor prescription rates., Conclusions: In this analysis of U.S. data from 2022 to 2023, SGLT2 inhibitor prescription among people with a Class 1a recommendation is low. Interventions are needed to increase uptake of guideline-recommended SGLT2 inhibitor use., Competing Interests: Funding Support and Author Disclosures This study was funded by R01 DK115534, K24HL155861, and K01DK121825 from the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health. The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2024 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Rationale & Objective: In 2021, the new Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) updated the creatinine-based estimated glomerular filtration rate (eGFR) equation and removed the coefficient for race. The development and validation of this equation involved binarizing race into African American and non-African American, involving few Asian participants. This study aimed to examine the difference between the 2021 equation and the previous 2009 equation on CKD prevalence estimates in 2 Asian populations., Study Design: Observational study using 2 national surveys., Setting & Participants: Participants from the 2019 Korea National Health and Nutrition Survey and participants self-reported as Asian from the 2011-2020 US National Health and Nutrition Survey., Exposure: eGFR using 2009 and 2021 CKD-EPI creatinine equation., Outcomes: Prevalence of CKD (eGFR <60 mL/min/1.73 m 2 or urine albumin-creatinine ratio ≥30 mg/g)., Analytical Approach: Sampling-weighted prevalence estimated using the 2009 and 2021 equations as well as the percentage of individuals with CKD G3+ using the 2009 equation being reclassified as not having CKD G3+ using the 2021 equation., Results: The prevalence of CKD estimated using the 2021 equation was 9.75% (95% confidence intervals [CI], 8.80-10.80%) in Koreans and 11.60% (95% CI, 10.23-13.13%) in US Asians. The prevalence of CKD estimated using the 2021 equation was slightly lower than that using the 2009 equation in both Korean and US Asian populations by 0.63% (95% CI, 0.44-0.90%) and 0.84% (95% CI, 0.52-1.34%), respectively. Furthermore, 32.8% and 30.2% of Koreans and US Asians with CKD G3-5, respectively, estimated using the 2009 equation were reclassified as not having CKD G3-5 when the eGFR was calculated using the 2021 equation., Limitations: Measured GFR was not available., Conclusions: Use of the 2021 CKD-EPI creatinine equation leads to a small decrease in CKD prevalence in both Korean and US Asian populations, and of similar magnitude, resulting in significant reclassification among those originally classified as having CKD G3+., (© 2024 The Authors.)

Accurate assessment of GFR is crucial to guiding drug eligibility, dosing of systemic therapy, and minimizing the risks of both undertreatment and toxicity in patients with cancer. Up to 32% of patients with cancer have baseline CKD, and both malignancy and treatment may cause kidney injury and subsequent CKD. To date, there has been lack of guidance to standardize approaches to GFR estimation in the cancer population. In this two-part statement from the American Society of Onco-Nephrology, we present key messages for estimation of GFR in patients with cancer, including the choice of GFR estimating equation, use of race and body surface area adjustment, and anticancer drug dose-adjustment in the setting of CKD. These key messages are based on a systematic review of studies assessing GFR estimating equations using serum creatinine and cystatin C in patients with cancer, against a measured GFR comparator. The preponderance of current data involving validated GFR estimating equations involves the CKD Epidemiology Collaboration (CKD-EPI) equations, with 2508 patients in whom CKD-EPI using serum creatinine and cystatin C was assessed (eight studies) and 15,349 in whom CKD-EPI with serum creatinine was assessed (22 studies). The former may have improved performance metrics and be less susceptible to shortfalls of eGFR using serum creatinine alone. Since included studies were moderate quality or lower, the American Society of Onco-Nephrology Position Committee rated the certainty of evidence as low. Additional studies are needed to assess the accuracy of other validated eGFR equations in patients with cancer. Given the importance of accurate and timely eGFR assessment, we advocate for the use of validated GFR estimating equations incorporating both serum creatinine and cystatin C in patients with cancer. Measurement of GFR via exogenous filtration markers should be considered in patients with cancer for whom eGFR results in borderline eligibility for therapies or clinical trials., (Copyright © 2024 by the American Society of Nephrology.)

Background: Early trials of dihydropyridine calcium channel blockers (DCCBs) suggest a detrimental effect on intraglomerular pressure and an association with albuminuria., Objective: We sought to evaluate the associations of DCCB initiation with albuminuria and kidney failure with replacement therapy (KFRT) and to determine whether renin-angiotensin system (RAS) blockade modified these associations., Design: We conducted a target trial emulation study using a new user, active comparator design and electronic health record data from Geisinger Health., Participants: We included patients without severe albuminuria or KFRT who were initiated on a DCCB or thiazide (active comparator) between January 1, 2004, and December 31, 2019., Main Measures: Using inverse probability of treatment weighting, we performed doubly robust Cox proportional hazards regression to estimate the association of DCCB initiation with incident severe albuminuria (urine albumin to creatinine ratio > 300 mg/g) and KFRT, overall and stratified by RAS blocker use., Key Results: There were 11,747 and 26,758 eligible patients initiating a DCCB and thiazide, respectively, with a weighted baseline mean age of 60 years, systolic blood pressure of 143 mm Hg, and eGFR of 86 mL/min/1.73 m 2 , and with a mean follow-up of 8 years. Compared with thiazides, DCCBs were significantly associated with the development of severe albuminuria (hazard ratio [HR], 1.29; 95% confidence interval [CI], 1.16-1.43), with attenuation of risk in the presence of RAS blockade (P for interaction < 0.001). The risk of KFRT was increased among patients without RAS blockade (HR, 1.66; 95% CI, 1.19-2.31), but not with RAS blockade (P for interaction = 0.005)., Conclusions: DCCBs were associated with increased risk of albuminuria and, in the absence of RAS blockade, KFRT. These findings suggest coupling DCCB therapy with RAS blockade may mitigate adverse kidney outcomes., (© 2024. The Author(s), under exclusive licence to Society of General Internal Medicine.)

Background: In patients with advanced chronic kidney disease (CKD), the effects of initiating treatment with an angiotensin-converting enzyme inhibitor (ACEi) or angiotensin-receptor blocker (ARB) on the risk for kidney failure with replacement therapy (KFRT) and death remain unclear., Purpose: To examine the association of ACEi or ARB treatment initiation, relative to a non-ACEi or ARB comparator, with rates of KFRT and death., Data Sources: Ovid Medline and the Chronic Kidney Disease Epidemiology Collaboration Clinical Trials Consortium from 1946 through 31 December 2023., Study Selection: Completed randomized controlled trials testing either an ACEi or an ARB versus a comparator (placebo or antihypertensive drugs other than ACEi or ARB) that included patients with a baseline estimated glomerular filtration rate (eGFR) below 30 mL/min/1.73 m 2 ., Data Extraction: The primary outcome was KFRT, and the secondary outcome was death before KFRT. Analyses were done using Cox proportional hazards models according to the intention-to-treat principle. Prespecified subgroup analyses were done according to baseline age (<65 vs. ≥65 years), eGFR (<20 vs. ≥20 mL/min/1.73 m 2 ), albuminuria (urine albumin-creatinine ratio <300 vs. ≥300 mg/g), and history of diabetes., Data Synthesis: A total of 1739 participants from 18 trials were included, with a mean age of 54.9 years and mean eGFR of 22.2 mL/min/1.73 m 2 , of whom 624 (35.9%) developed KFRT and 133 (7.6%) died during a median follow-up of 34 months (IQR, 19 to 40 months). Overall, ACEi or ARB treatment initiation led to lower risk for KFRT (adjusted hazard ratio, 0.66 [95% CI, 0.55 to 0.79]) but not death (hazard ratio, 0.86 [CI, 0.58 to 1.28]). There was no statistically significant interaction between ACEi or ARB treatment and age, eGFR, albuminuria, or diabetes ( P for interaction > 0.05 for all)., Limitation: Individual participant-level data for hyperkalemia or acute kidney injury were not available., Conclusion: Initiation of ACEi or ARB therapy protects against KFRT, but not death, in people with advanced CKD., Primary Funding Source: National Institutes of Health. (PROSPERO: CRD42022307589)., Competing Interests: Disclosures: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M23-3236.

People living with chronic kidney disease (CKD) often experience multimorbidity and require polypharmacy. Kidney dysfunction can also alter the pharmacokinetics and pharmacodynamics of medications, which can modify their risks and benefits; the extent of these changes is not well understood for all situations or medications. The principle of drug stewardship is aimed at maximizing medication safety and effectiveness in a population of patients through a variety of processes including medication reconciliation, medication selection, dose adjustment, monitoring for effectiveness and safety, and discontinuation (deprescribing) when no longer necessary. This Review is aimed at serving as a resource for achieving optimal drug stewardship for patients with CKD. We describe special considerations for medication use during pregnancy and lactation, during acute illness and in patients with cancer, as well as guidance for the responsible use of over-the-counter drugs, herbal remedies, supplements and sick-day rules. We also highlight inequities in medication access worldwide and suggest policies to improve access to quality and essential medications for all persons with CKD. Further strategies to promote drug stewardship include patient education and engagement, the use of digital health tools, shared decision-making and collaboration within interdisciplinary teams. Throughout, we position the person with CKD at the centre of all drug stewardship efforts., (© 2024. Springer Nature Limited.)

Background: Glucagon-like peptide-1 receptor agonists (GLP-1RA) have cardiovascular benefits in type 2 diabetes, but none of the cardiovascular trials studied atrial fibrillation/atrial flutter (AF) as a primary endpoint. Data from post-marketing surveillance studies remains sparse., Objective: To examine the real-world risk of AF comparing GLP-1RA with other non-insulin glucose-lowering agents., Design: Cohort study using de-identified electronic health record data from the Optum Labs Data Warehouse., Participants: Adult patients with diabetes who were newly prescribed add-on non-insulin glucose-lowering agents and were on metformin between 2005-2020., Exposures: New users of GLP-1RA were separately compared with new users of dipeptidyl peptidase-4 inhibitors (DPP4i) and sodium-glucose cotransporter 2 inhibitors (SGLT2i), using 1:1 propensity score matching to adjust for differences in patient characteristics., Main Measures: The primary outcome was incident AF, defined and captured by diagnosis code for AF. Incidence rate difference (IRD) and hazard ratio (HR) were estimated in the matched cohorts., Key Results: In the matched cohort of 14,566 pairs of GLP-1RA and DPP4i followed for a median of 3.8 years, GLP-1RA use was associated with a lower risk of AF (IRD, -1.0; 95% CI, -1.8 to -0.2 per 1000 person-years; HR, 0.82; 95% CI, 0.70 to 0.96). In the matched cohort of 9,424 pairs of patients on GLP-1RA and SGLT2i with a median follow-up of 2.9 years, there was no difference in the risk for AF (IRD, 0.4; 95% CI -0.7 to 1.5 per 1000 person-years; HR, 1.12; 95% CI, 0.89 to 1.42)., Conclusions: In this real-word study, GLP-1RA was associated with a lower risk of AF compared with DPP4i, but no difference compared with SGLT2i, suggesting that cardiovascular benefits of GLP-1RA use may extend to prevention for AF in patients with diabetes. Our findings call for future randomized controlled trials to focus on the effects of GLP-1RA on AF prevention., (© 2024. The Author(s), under exclusive licence to Society of General Internal Medicine.)

Background: There is interest in identifying novel filtration markers that lead to more accurate GFR estimates than current markers (creatinine and cystatin C) and are more consistent across demographic groups. We hypothesize that large-scale metabolomics can identify serum metabolites that are strongly influenced by glomerular filtration rate (GFR) and are more consistent across demographic variables than creatinine, which would be promising filtration markers for future investigation., Methods: We evaluated the consistency of associations between measured GFR (mGFR) and 887 common, known metabolites quantified by an untargeted chromatography- and spectroscopy-based metabolomics platform (Metabolon) performed on frozen blood samples from 580 participants in Chronic Kidney Disease in Children (CKiD), 674 participants in Modification of Diet in Renal Disease (MDRD) Study and 962 participants in African American Study of Kidney Disease and Hypertension (AASK). We evaluated metabolite-mGFR correlation association with metabolite class, molecular weight, assay platform and measurement coefficient of variation (CV). Among metabolites with strong negative correlations with mGFR ( r < -0.5), we assessed additional variation by age (height in children), sex, race and body mass index (BMI)., Results: A total of 561 metabolites (63%) were negatively correlated with mGFR. Correlations with mGFR were highly consistent across study, sex, race and BMI categories (correlation of metabolite-mGFR correlations between 0.88 and 0.95). Amino acids, carbohydrates and nucleotides were more often negatively correlated with mGFR compared with lipids, but there was no association with metabolite molecular weight, liquid chromatography/mass spectrometry platform and measurement CV. Among 114 metabolites with strong negative associations with mGFR ( r < -0.5), 27 were consistently not associated with age (height in children), sex or race., Conclusions: The majority of metabolite-mGFR correlations were negative and consistent across sex, race, BMI and study. Metabolites with consistent strong negative correlations with mGFR and non-association with demographic variables may represent candidate markers to improve estimation of GFR., Competing Interests: The authors declare no conflict of interest relevant to the data presented in this manuscript., (© The Author(s) 2024. Published by Oxford University Press on behalf of the ERA.)

The Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease (CKD) updates the KDIGO 2012 guideline and has been developed with patient partners, clinicians, and researchers around the world, using robust methodology. This update, based on a substantially broader base of evidence than has previously been available, reflects an exciting time in nephrology. New therapies and strategies have been tested in large and diverse populations that help to inform care; however, this guideline is not intended for people receiving dialysis nor those who have a kidney transplant. The document is sensitive to international considerations, CKD across the lifespan, and discusses special considerations in implementation. The scope includes chapters dedicated to the evaluation and risk assessment of people with CKD, management to delay CKD progression and its complications, medication management and drug stewardship in CKD, and optimal models of CKD care. Treatment approaches and actionable guideline recommendations are based on systematic reviews of relevant studies and appraisal of the quality of the evidence and the strength of recommendations which followed the "Grading of Recommendations Assessment, Development, and Evaluation" (GRADE) approach. The limitations of the evidence are discussed. The guideline also provides practice points, which serve to direct clinical care or activities for which a systematic review was not conducted, and it includes useful infographics and describes an important research agenda for the future. It targets a broad audience of people with CKD and their healthcare, while being mindful of implications for policy and payment., (Copyright © 2023 Kidney Disease: Improving Global Outcomes (KDIGO). Published by Elsevier Inc. All rights reserved.)

Background: New equations to estimate glomerular filtration rate based on creatinine (eGFRcr), cystatin C (eGFRcys) or both (eGFRcr-cys) have been developed by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and the European Kidney Function Consortium (EKFC). There is a need to evaluate the performance of these equations in diverse European settings to inform implementation decisions, especially among people with key comorbid conditions., Methods: We performed a cross-sectional study including 6174 adults referred for single-point plasma clearance of iohexol in Stockholm, Sweden, with 9579 concurrent measurements of creatinine and cystatin C. We assessed the performance of the CKD-EPI 2009/2012/2021, EKFC 2021/2023, revised Lund-Malmö (RLM) 2011 and Caucasian, Asian, Pediatric and Adult (CAPA) 2014 equations against measured GFR (mGFR)., Results: Mean age was 56 years, median mGFR was 62 mL/min/1.73 m2 and 40% were female. Comorbid conditions were common: cardiovascular disease (30%), liver disease (28%), diabetes (26%) and cancer (26%). All eGFRcr-cys equations had small bias and P30 (the percentage of estimated values within 30% of mGFR) close to 90%, and performed better than eGFRcr or eGFRcys equations. Among eGFRcr equations, CKD-EPI 2009 and CKD-EPI 2021 showed larger bias and lower P30 than EKFC 2021 and RLM. There were no meaningful differences in performance across eGFRcys equations. Findings were consistent across comorbid conditions, and eGFRcr-cys equations showed good performance in patients with liver disease, cancer and heart failure., Conclusions: In conclusion, eGFRcr-cys equations performed best, with minimal variation among equations in this Swedish cohort. The lower performance of CKD-EPI eGFRcr equations compared with EKFC and RLM may reflect differences in population characteristics and mGFR methods. Implementing eGFRcr equations will require a trade-off between accuracy and uniformity across regions., (© The Author(s) 2023. Published by Oxford University Press on behalf of the ERA.)

Significance Statement: Metabolic acidosis is a common complication of CKD and is associated with more rapid decline of kidney function, but well-powered controlled randomized trials testing the effect of treating metabolic acidosis on slowing CKD progression have not been conducted. The VALOR-CKD study randomized 1480 individuals with CKD and metabolic acidosis, across 320 sites to placebo or veverimer (a novel hydrochloric acid binder). The findings did not demonstrate the efficacy of veverimer in slowing CKD progression, but the difference in serum bicarbonate between placebo and drug arms was only approximately 1 mEq/L. Veverimer was safe and well tolerated., Background: Metabolic acidosis is common in CKD, but whether its treatment slows CKD progression is unknown. Veverimer, a novel hydrochloric acid binder that removes acid from the gastrointestinal tract, leads to an increase in serum bicarbonate., Methods: In a phase 3, double-blind, placebo-controlled trial, patients with CKD (eGFR of 20-40 ml/min per 1.73 m 2 ) and metabolic acidosis (serum bicarbonate of 12-20 mEq/L) from 35 countries were randomized to veverimer or placebo. The primary outcome was the composite end point of CKD progression, defined as the development of ESKD (kidney transplantation or maintenance dialysis), a sustained decline in eGFR of ≥40% from baseline, or death due to kidney failure., Results: The mean (±SD) baseline eGFR was 29.2±6.3 ml/min per 1.73 m 2 , and serum bicarbonate was 17.5±1.4 mEq/L; this increased to 23.4±2.0 mEq/L after the active treatment run-in. After randomized withdrawal, the mean serum bicarbonate was 22.0±3.0 mEq/L and 20.9±3.3 mEq/L in the veverimer and placebo groups at month 3, and this approximately 1 mEq/L difference remained stable for the first 24 months. A primary end point event occurred in 149/741 and 148/739 patients in the veverimer and placebo groups, respectively (hazard ratio, 0.99; 95% confidence interval, 0.8 to 1.2; P = 0.90). Serious and overall adverse event incidence did not differ between the groups., Conclusions: Among patients with CKD and metabolic acidosis, treatment with veverimer did not slow CKD progression. The lower than expected bicarbonate separation may have hindered the ability to test the hypothesis., Clinical Trial Registry Name and Registration Number: VALOR-CKD, NCT03710291 ., (Copyright © 2024 by the American Society of Nephrology.)

Background: The commonly accepted threshold of glomerular filtration rate (GFR) to define chronic kidney disease (CKD) is less than 60 mL/min/1.73 m 2 . This threshold is based partly on associations between estimated GFR (eGFR) and the frequency of adverse outcomes. The association is weaker in older adults, which has created disagreement about the appropriateness of the threshold for these persons. In addition, the studies measuring these associations included relatively few outcomes and estimated GFR on the basis of creatinine level (eGFR cr ), which may be less accurate in older adults., Objective: To evaluate associations in older adults between eGFR cr versus eGFR based on creatinine and cystatin C levels (eGFR cr-cys ) and 8 outcomes., Design: Population-based cohort study., Setting: Stockholm, Sweden, 2010 to 2019., Participants: 82 154 participants aged 65 years or older with outpatient creatinine and cystatin C testing., Measurements: Hazard ratios for all-cause mortality, cardiovascular mortality, and kidney failure with replacement therapy (KFRT); incidence rate ratios for recurrent hospitalizations, infection, myocardial infarction or stroke, heart failure, and acute kidney injury., Results: The associations between eGFR cr-cys and outcomes were monotonic, but most associations for eGFR cr were U-shaped. In addition, eGFR cr-cys was more strongly associated with outcomes than eGFR cr . For example, the adjusted hazard ratios for 60 versus 80 mL/min/1.73 m 2 for all-cause mortality were 1.2 (95% CI, 1.1 to 1.3) for eGFR cr-cys and 1.0 (CI, 0.9 to 1.0) for eGFR cr , and for KFRT they were 2.6 (CI, 1.2 to 5.8) and 1.4 (CI, 0.7 to 2.8), respectively. Similar findings were observed in subgroups, including those with a urinary albumin-creatinine ratio below 30 mg/g., Limitation: No GFR measurements., Conclusion: Compared with low eGFR cr in older patients, low eGFR cr-cys was more strongly associated with adverse outcomes and the associations were more uniform., Primary Funding Source: Swedish Research Council, National Institutes of Health, and Dutch Kidney Foundation., Competing Interests: Disclosures: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M23-1138.

Creatinine and cystatin-C are recommended for estimating glomerular filtration rate (eGFR) but accuracy is suboptimal. Here, using untargeted metabolomics data, we sought to identify candidate filtration markers for a new targeted assay using a novel approach based on their maximal joint association with measured GFR (mGFR) and with flexibility to consider their biological properties. We analyzed metabolites measured in seven diverse studies encompasing 2,851 participants on the Metabolon H4 platform that had Pearson correlations with log mGFR and used a stepwise approach to develop models to < -0.5 estimate mGFR with and without inclusion of creatinine that enabled selection of candidate markers. In total, 456 identified metabolites were present in all studies, and 36 had correlations with mGFR < -0.5. A total of 2,225 models were developed that included these metabolites; all with lower root mean square errors and smaller coefficients for demographic variables compared to estimates using untargeted creatinine. Seventeen metabolites were chosen, including 12 new candidate filtration markers. The selected metabolites had strong associations with mGFR and little dependence on demographic factors. Candidate metabolites were identified with maximal joint association with mGFR and minimal dependence on demographic variables across many varied clinical settings. These metabolites are excreted in urine and represent diverse metabolic pathways and tubular handling. Thus, our data can be used to select metabolites for a multi-analyte eGFR determination assay using mass spectrometry that potentially offers better accuracy and is less prone to non-GFR determinants than the current eGFR biomarkers., (Copyright © 2023 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Background: Surrogate endpoints, such as those of interest in chronic kidney disease (CKD), are often evaluated using Bayesian meta-regression. Trials used for the analysis can evaluate a variety of interventions for different sub-classifications of disease, which can introduce two additional goals in the analysis. The first is to infer the quality of the surrogate within specific trial subgroups defined by disease or intervention classes. The second is to generate more targeted subgroup-specific predictions of treatment effects on the clinical endpoint., Methods: Using real data from a collection of CKD trials and a simulation study, we contrasted surrogate endpoint evaluations under different hierarchical Bayesian approaches. Each approach we considered induces different assumptions regarding the relatedness (exchangeability) of trials within and between subgroups. These include partial-pooling approaches, which allow subgroup-specific meta-regressions and, yet, facilitate data adaptive information sharing across subgroups to potentially improve inferential precision. Because partial-pooling models come with additional parameters relative to a standard approach assuming one meta-regression for the entire set of studies, we performed analyses to understand the impact of the parameterization and priors with the overall goals of comparing precision in estimates of subgroup-specific meta-regression parameters and predictive performance., Results: In the analyses considered, partial-pooling approaches to surrogate endpoint evaluation improved accuracy of estimation of subgroup-specific meta-regression parameters relative to fitting separate models within subgroups. A random rather than fixed effects approach led to reduced bias in estimation of meta-regression parameters and in prediction in subgroups where the surrogate was strong. Finally, we found that subgroup-specific meta-regression posteriors were robust to use of constrained priors under the partial-pooling approach, and that use of constrained priors could facilitate more precise prediction for clinical effects in trials of a subgroup not available for the initial surrogacy evaluation., Conclusion: Partial-pooling modeling strategies should be considered for surrogate endpoint evaluation on collections of heterogeneous studies. Fitting these models comes with additional complexity related to choosing priors. Constrained priors should be considered when using partial-pooling models when the goal is to predict the treatment effect on the clinical endpoint., (© 2024. The Author(s).)

Background: The growth of oral muscle relaxant prescriptions among older adults in the United States is concerning due to the drugs' adverse sedative effects. Baclofen is a gamma-aminobutyric acid agonist muscle relaxant that is associated with encephalopathy. We characterized the risk of fall and fracture associated with oral baclofen against other muscle relaxants (tizanidine or cyclobenzaprine) in older adults., Methods: We designed a new-user, active-comparator study using tertiary health system data from Geisinger Health, Pennsylvania (January 2005 through December 2018). Older adults (aged ≥65 years) newly treated with baclofen, tizanidine, or cyclobenzaprine were included. Propensity score-based inverse probability of treatment weighting (IPTW) was used to balance the treatment groups on 58 baseline characteristics. Fine-Gray competing risk regression was used to estimate the risk of fall and fracture., Results: The study cohort comprised of 2205 new baclofen users, 1103 new tizanidine users, and 9708 new cyclobenzaprine users. During a median follow-up of 100 days, baclofen was associated with a higher risk of fall compared to tizanidine (IPTW incidence rate, 108.4 vs. 61.9 per 1000 person-years; subdistribution hazard ratio [SHR], 1.68 [95% CI, 1.20-2.36]). The risk of fall associated with baclofen was comparable to cyclobenzaprine (SHR, 1.17 [95% CI, 0.93-1.47]) with a median follow-up of 106 days. The risk of fracture was similar among patients treated with baclofen versus tizanidine (SHR, 0.85 [95% CI, 0.63-1.14]) or cyclobenzaprine (SHR, 0.85 [95% CI, 0.67-1.07])., Conclusions: The risk of fall associated with baclofen was greater than tizanidine, but not compared to cyclobenzaprine in older adults. The risk of fracture was comparable among the older users of baclofen, tizanidine, and cyclobenzaprine. Our findings may inform risk-benefit considerations in the increasingly common clinical encounters where oral muscle relaxants are prescribed., (© 2023 The American Geriatrics Society.)

Significance Statement: New eGFR equations from Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and European Kidney Function Consortium (EKFC) using creatinine (eGFRcr), cystatin C (eGFRcys), and both (eGFRcr-cys) have sufficient accuracy for use in clinical practice, leading to uncertainty in selecting equations for implementation. The authors evaluated performance of equations in an independent population of 4050 adults and evaluated other considerations important for implementation. They found that CKD-EPI and EKFC equations are approaching convergence, with better performance of eGFRcr-cys equations in the overall group and fewer differences among race, sex, and age subgroups than eGFRcr equations. Larger differences among eGFRcr equations reflect regional population differences in creatinine, forcing a trade-off between accuracy and uniformity in global implementation of eGFRcr equations. More widespread use of cystatin C could avoid this trade-off., Background: New CKD-EPI and EKFC eGFR equations using eGFRcr, eGFRcys, and both (eGFRcr-cys) have sufficient accuracy for use in clinical practice. A better understanding of the equations, including their performance in race, sex and age subgroups, is important for selection of eGFR equations for global implementation., Methods: We evaluated performance (bias and P 30 ) of equations and methods used for equation development in an independent study population comprising 4050 adults pooled from 12 studies. The mean (SD) measured GFR was 76.4 (29.6) ml/min per 1.73 m 2 and age 57.0 (17.4) years, with 1557 (38%) women and 579 (14%) Black participants., Results: Coefficients for creatinine, cystatin C, age, and sex in the CKD-EPI and EKFC equations are similar. Performance of the eGFRcr-cys equations in the overall population (bias <±5 ml/min per 1.73 m 2 and P 30 >90%) was better than the eGFRcr or eGFRcys equations, with fewer differences among race, sex, and age subgroups. Differences in performance across subgroups reflected differences in diversity of source populations and use of variables for race and sex for equation development. Larger differences among eGFRcr equations reflected regional population differences in non-GFR determinants of creatinine., Conclusion: CKD-EPI and EKFC equations are approaching convergence. It is not possible to maximize both accuracy and uniformity in selecting one of the currently available eGFRcr equations for implementation across regions. Decisions should consider methods for equation development in addition to performance. Wider use of cystatin C with creatinine could maximize both accuracy and uniformity of GFR estimation using currently available equations., (Copyright © 2023 by the American Society of Nephrology.)

Background: Recommendations for apixaban dosing on the basis of kidney function are inconsistent between the US Food and Drug Administration and European Medicines Agency for patients with atrial fibrillation. Optimal apixaban dosing in chronic kidney disease remains unknown., Methods: With the use of deidentified electronic health record data from the Optum Labs Data Warehouse, patients with atrial fibrillation and chronic kidney disease stage 4/5 initiating apixaban between 2013 and 2021 were identified. Risks of bleeding and stroke/systemic embolism were compared by apixaban dose (5 versus 2.5 mg), adjusted for baseline characteristics by the inverse probability of treatment weighting. The Fine-Gray subdistribution hazard model was used to account for the competing risk of death. Cox regression was used to examine risk of death by apixaban dose., Results: Among 4313 apixaban new users, 1705 (40%) received 5 mg and 2608 (60%) received 2.5 mg. Patients treated with 5 mg apixaban were younger (mean age, 72 versus 80 years), with greater weight (95 versus 80 kg) and higher serum creatinine (2.7 versus 2.5 mg/dL). Mean estimated glomerular filtration rate was not different between the groups (24 versus 24 mL·min -1 ·1.73 m -2 ). In inverse probability of treatment weighting analysis, apixaban 5 mg was associated with a higher risk of bleeding (incidence rate 4.9 versus 2.9 events per 100 person-years; incidence rate difference, 2.0 [95% CI, 0.6-3.4] events per 100 person-years; subdistribution hazard ratio, 1.63 [95% CI, 1.04-2.54]). There was no difference between apixaban 5 mg and 2.5 mg groups in the risk of stroke/systemic embolism (3.3 versus 3.0 events per 100 person-years; incidence rate difference, 0.2 [95% CI, -1.0 to 1.4] events per 100 person-years; subdistribution hazard ratio, 1.01 [95% CI, 0.59-1.73]), or death (9.9 versus 9.4 events per 100 person-years; incidence rate difference, 0.5 [95% CI, -1.6 to 2.6] events per 100 person-years; hazard ratio, 1.03 [95% CI, 0.77-1.38])., Conclusions: Compared with 2.5 mg, use of 5 mg apixaban was associated with a higher risk of bleeding in patients with atrial fibrillation and severe chronic kidney disease, with no difference in the risk of stroke/systemic embolism or death, supporting the apixaban dosing recommendations on the basis of kidney function by the European Medicines Agency, which differ from those issued by the US Food and Drug Administration., Competing Interests: Disclosures Dr Chang reports having consultancy agreements with Amgen, Novartis, and Reata; receiving research funding from a Novo Nordisk Investigator Sponsored Study; having an advisory or leadership role with Reata, Relypsa; and having other interests or relationships with National Kidney Foundation grant support and the NKF Patient Network. Dr Inker reports having consultancy agreements with Diamtrix; receiving research funding to the institution for research and contracts with the National Institutes of Health, National Kidney Foundation, Omeros, Reata Pharmaceuticals; having consulting agreements to her institution with Omeros and Tricida Inc.; having an advisory or leadership role with the Alport Syndrome Foundation; and having other interests or relationships as a member of the American Society of Nephrology, the National Kidney Disease Education Program, and the National Kidney Foundation. Dr Grams reports having an advisory or leadership role with AJKD, CJASN, JASN Editorial Board, KDIGO Executive Committee, NKF Scientific Advisory Board, and the USRDS Scientific Advisory Board; and having other interests or relationships with grant funding from NKF, which receives funding from multiple pharmaceutical companies, and grant funding from the National Institutes of Health. Dr Shin reports receiving research funding from Merck and the National Institutes of Health.

Rationale & Objective: Cystatin C is recommended for measuring estimated glomerular filtration rate (eGFR) when estimates based on creatinine (eGFR cr ) are not thought to be accurate enough for clinical decision making. While global adoption is slow, routine cystatin C testing in Sweden has been available for over a decade, providing real-world evidence about the magnitude of differences between eGFR cys and eGFR cr and their association with clinical outcomes., Study Design: Observational study., Setting & Participants: 158,601 adults (48% women; mean age 62 years, eGFR cr 80, and eGFR cys 73mL/min/1.73/m 2 ) undergoing testing for creatinine and cystatin C on the same day in connection with a health care encounter during 2010-2018 in Stockholm, Sweden., Exposure: Percentage difference of eGFR cys minus eGFR cr (eGFR diff )., Outcome: Kidney failure with replacement therapy (KFRT), acute kidney injury (AKI), atherosclerotic cardiovascular disease (ASCVD), heart failure, and death., Analytical Approach: Multivariable Cox proportional hazards regression., Results: Discordances between eGFR cr and eGFR cys were common, with eGFR cys being lower than eGFR cr (negative eGFR diff ) in most cases (65%). Patients with larger negative eGFR diff were older, more often female, with higher eGFR cr and albuminuria, and more comorbid conditions. Compared with patients with similar eGFR cys and eGFR cr , the lowest quartile (eGFR cys > 27% lower than eGFR cr ) had the higher HR of all study outcomes: AKI, 2.6 (95% CI, 2.4-2.9); KFRT, 1.4 (95% CI, 1.2-1.6); ASCVD, 1.4 (95% CI, 1.3-1.5); heart failure, 2.0 (95% CI, 1.9-2.2); and all-cause death, 2.6 (95% CI, 2.5-2.7). Conversely, patients in the highest quartile (positive eGFR diff ) were at lower risk., Limitations: Observational study, lack of information on indications for cystatin C testing., Conclusions: Cystatin C testing in routine care shows that many patients have a lower eGFR cys than eGFR cr , and these patients have a higher risk of multiple adverse outcomes., Plain-Language Summary: Clinicians require guidance when there are discrepancies between the estimated glomerular filtration rate based on creatinine (eGFR cr ) and based on cystatin C (eGFR cys ) in the same individual. Routine cystatin C testing in Sweden for over a decade permits exploration of how common and large these discrepancies are, and their associations with adverse clinical outcomes. In this observational study, we found that discordances between eGFR cys and eGFR cr are common, and 1 in 4 patients tested had an eGFR cys > 28% lower than their eGFR cr . We also show that an eGFR cys that is lower than the eGFR cr consistently identifies patients at higher risk of adverse outcomes, including cardiovascular events, kidney replacement therapy, acute kidney injury, and death., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Importance: Chronic kidney disease (low estimated glomerular filtration rate [eGFR] or albuminuria) affects approximately 14% of adults in the US., Objective: To evaluate associations of lower eGFR based on creatinine alone, lower eGFR based on creatinine combined with cystatin C, and more severe albuminuria with adverse kidney outcomes, cardiovascular outcomes, and other health outcomes., Design, Setting, and Participants: Individual-participant data meta-analysis of 27 503 140 individuals from 114 global cohorts (eGFR based on creatinine alone) and 720 736 individuals from 20 cohorts (eGFR based on creatinine and cystatin C) and 9 067 753 individuals from 114 cohorts (albuminuria) from 1980 to 2021., Exposures: The Chronic Kidney Disease Epidemiology Collaboration 2021 equations for eGFR based on creatinine alone and eGFR based on creatinine and cystatin C; and albuminuria estimated as urine albumin to creatinine ratio (UACR)., Main Outcomes and Measures: The risk of kidney failure requiring replacement therapy, all-cause mortality, cardiovascular mortality, acute kidney injury, any hospitalization, coronary heart disease, stroke, heart failure, atrial fibrillation, and peripheral artery disease. The analyses were performed within each cohort and summarized with random-effects meta-analyses., Results: Within the population using eGFR based on creatinine alone (mean age, 54 years [SD, 17 years]; 51% were women; mean follow-up time, 4.8 years [SD, 3.3 years]), the mean eGFR was 90 mL/min/1.73 m2 (SD, 22 mL/min/1.73 m2) and the median UACR was 11 mg/g (IQR, 8-16 mg/g). Within the population using eGFR based on creatinine and cystatin C (mean age, 59 years [SD, 12 years]; 53% were women; mean follow-up time, 10.8 years [SD, 4.1 years]), the mean eGFR was 88 mL/min/1.73 m2 (SD, 22 mL/min/1.73 m2) and the median UACR was 9 mg/g (IQR, 6-18 mg/g). Lower eGFR (whether based on creatinine alone or based on creatinine and cystatin C) and higher UACR were each significantly associated with higher risk for each of the 10 adverse outcomes, including those in the mildest categories of chronic kidney disease. For example, among people with a UACR less than 10 mg/g, an eGFR of 45 to 59 mL/min/1.73 m2 based on creatinine alone was associated with significantly higher hospitalization rates compared with an eGFR of 90 to 104 mL/min/1.73 m2 (adjusted hazard ratio, 1.3 [95% CI, 1.2-1.3]; 161 vs 79 events per 1000 person-years; excess absolute risk, 22 events per 1000 person-years [95% CI, 19-25 events per 1000 person-years])., Conclusions and Relevance: In this retrospective analysis of 114 cohorts, lower eGFR based on creatinine alone, lower eGFR based on creatinine and cystatin C, and more severe UACR were each associated with increased rates of 10 adverse outcomes, including adverse kidney outcomes, cardiovascular diseases, and hospitalizations.