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Introduction Exposure concentrations assessed from spot urine samples are typically adjusted to a constant creatinine concentration to correct for dilution of the samples due to the variable hydration status of [...], Introduction: A commonly used approach to adjust for urine dilution in analyses of biomarkers is to adjust for urinary creatinine. However, creatinine is a product of muscle mass and is therefore associated with body mass. In studies of urinary analytes and obesity or obesity-related outcomes, controlling for creatinine could induce collider stratification bias. We illustrate this phenomenon with an analysis of urinary arsenic. Objective: We aimed to evaluate various approaches of adjustment for urinary dilution on the associations between urinary arsenic concentration and measures of obesity. Methods: Using data from the National Health and Nutrition Examination Survey, we regressed body mass index (BMI) and waist-to-height ratios on urinary arsenic concentrations. We compared eight approaches to account for urine dilution, including standardization by urinary creatinine, osmolality, and flow rates, and inclusion of these metrics as independent covariates. We also used a recently proposed method known as covariate-adjusted standardization. Results: Inverse associations between urinary arsenic concentration with BMI and waist-to-height ratio were observed when either creatinine or osmolality were used to standardize or as covariates. Not adjusting for dilution, standardizing or adjusting for urinary flow rate, and using covariate-adjusted standardization resulted in null associations observed between arsenic concentration in relation to BMI and waist- to-height ratio. Conclusions: Our findings suggest that arsenic exposure is not associated with obesity, and that urinary creatinine and osmolality may be colliders on the causal pathway from arsenic exposure to obesity, as common descendants of hydration and body composition. In studies of urinary biomarkers and obesity or obesity-related outcomes, alternative metrics such as urinary flow rate or analytic strategies such as covariate-adjusted standardization should be considered. https://doi.org/10.1289/EHP1202

Although its efficacy in running, swimming, and nonlaboratory settings is inconclusive (1), creatine has become very popular among athletes. Some laboratory studies have shown oral creatine supplementation to be ergogenic [...]

Chronic kidney disease has been shown to adversely affect patients after total or partial nephrectomy in greater than 30% of cases. (1) Recent reports have highlighted the utility and value [...], Context.--Evaluating nontumor portions of tumor nephrectomies is useful to diagnose nonneoplastic renal disease. Objective.--To determine the medical renal disease frequency and to assess the prognostic significance of the various renal pathologic variables with long-term follow-up in tumor nephrectomy patients. Design.--We reviewed nonneoplastic kidney sections of 456 consecutive cases from 1998 to 2008. Seventy-five cases were excluded (19 tumor compression, 25 no nonneoplastic tissue, 22 embolized kidneys, 9 end stage). Special staining, immunofluorescence, and/or electron microscopy was performed where appropriate. Vascular sclerosis was scored from mild to severe; interstitial fibrosis/ tubular atrophy and global glomerulosclerosis (GS) were expressed as percentages. Follow-up, minimum 12 months, was evaluated in 156 cases. All renal pathologic variables were compared with regard to change in creatinine level from preoperative assessment to follow-up. Results.--Of 381 cases, 57 had additional medical renal disease (15%), most frequently diabetic nephropathy (28) and hypertensive nephropathy (11). Postoperative creatinine levels increased significantly in patients with severe arteriosclerosis or arteriolosclerosis, >5% GS, and >10% interstitial fibrosis/tubular atrophy. Seventy-four percent of cases with additional nonneoplastic diagnoses showed severe arteriolosclerosis. Higher corresponding GS was seen in the more affected vascular cases: mean, 5.56% GS for mild versus 23% GS for severe. Three patients progressed to renal failure 1 to 4 years after nephrectomy, 2 with hypertensive nephrosclerosis and 1 with diabetic nephropathy. Conclusions.--Medical renal disease was identified in 15% of tumor nephrectomy specimens. The degrees of vascular sclerosis, GS, and interstitial fibrosis/tubular atrophy are predictive of elevated creatinine levels in postnephrectomy patients. Prognostic implications of the nontumor pathology are important in nephrectomized patients. (Arch Pathol Lab Med. 2013;137:531-540; doi: 10.5858/arpa.2012-0070-OA)

Author(s): Donald J. Weaver[sup.1] [sup.2] , Annabelle Chua[sup.1] Author Affiliations: (1) Department of Pediatrics, Levine Children's Hospital at Carolinas Medical Center, 28232, Charlotte, NC, USA (2) Division of Nephrology and [...]