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We present a patient at risk of misdiagnosis with multiple myeloma due to pseudohypercalcemia. Examinations showed monoclonal protein, 50% monoclonal plasma cells in bone marrow, and hypercalcemia but no osteolytic bone lesions. Follow-up tests revealed pseudohypercalcemia, with elevated total calcium, but normal ionized calcium: a discrepancy due to calcium binding to monoclonal paraprotein (confirmed by laboratory experiments). Accordingly, the patient was diagnosed with smouldering myeloma. After 900 days, the presence of bone lesions prompted the start of treatment for myeloma. Consequently, monoclonal paraprotein levels declined and pseudohypercalcemia dissolved. Hence, ionized calcium should be measured in monoclonal gammopathies to avoid misdiagnosis., Competing Interests: The authors declare that they have no conflicts of interest., (Copyright © 2024 Svenja F. B. J. Mennens et al.)

Nucleic acid detection methods based on CRISPR and isothermal amplification techniques show great potential for point-of-care diagnostic applications. However, most current methods rely on fluorescent or lateral flow assay readout, requiring external excitation or postamplification reaction transfer. Here, we developed a bioluminescent nucleic acid sensor (LUNAS) platform in which target dsDNA is sequence-specifically detected by a pair of dCas9-based probes mediating split NanoLuc luciferase complementation. LUNAS is easily integrated with recombinase polymerase amplification (RPA), providing attomolar sensitivity in a rapid one-pot assay. A calibrator luciferase is included for a robust ratiometric readout, enabling real-time monitoring of the RPA reaction using a simple digital camera. We designed an RT-RPA-LUNAS assay that allows SARS-CoV-2 RNA detection without the need for cumbersome RNA isolation and demonstrated its diagnostic performance for COVID-19 patient nasopharyngeal swab samples. Detection of SARS-CoV-2 from samples with viral RNA loads of ∼200 cp/μL was achieved within ∼20 min, showing that RPA-LUNAS is attractive for point-of-care infectious disease testing., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Objective: Radiofrequency ablation (RFA) is increasingly considered the prime option for treating symptomatic, benign, non-functioning thyroid nodules (NFTN). However, little is known about the degree of operator experience required to achieve optimal results. This study describes the RFA learning curve of a single-center team., Methods: A retrospective cohort study of the first 103 patients receiving RFA treatment for a single, symptomatic, and benign NFTN, with a follow-up of at least 1 year. The primary outcome measure was technique efficacy, defined as the percentage of patients with a 6-month nodal volume reduction ratio (VRR) >50% after single-session RFA. Optimal treatment efficacy was defined as a 6-month VRR >50% achieved in at least 75% of patients. Secondary outcomes were complications of RFA and indications of secondary interventions., Results: Median nodal volume at baseline was 12.0 mL (range 2.0-58.0 mL). A 6-month VRR >50% was achieved in 45% of the first 20 patients, 75% of the next 20, and 79% of the following 63 patients. Complications included minor bleeding (N = 4), transient hyperthyroidism (N = 4), and transient loss of voice (N = 1). Poor volume reduction or nodular regrowth led to diagnostic lobectomy in 11 patients and a second RFA in 5. Lobectomy revealed a follicular carcinoma (T2N0M0) in 2 patients. In 1 patient, nodule regrowth was caused by an intranodular solitary B-cell lymphoma., Conclusion: About 40 procedures are required to achieve a 6-month VRR >50% in the majority of patients. Appropriate follow-up with re-evaluation is recommended for all patients with a VRR <50% and in those with regrowth to exclude underlying malignancy.

Background: Recently, a new model has been proposed to assess hydration in patients by measurement of total body electrical resistance (TBER), with results expressed in ohm rather than in liter body water. According to this approach, hydration is considered to be normal if TBER is within the normal range. As TBER is inversely related to the size of the limb muscle compartment, this relationship can be used to calculate the patient-specific TBER normal value (TBER norm ). The present study investigates whether the prediction of TBER norm can be improved by the use of ultrasound (US) instead of anthropometrically derived parameters of limb muscularity., Methods: In total, 129 healthy subjects (60 men and 69 women) ranging in age from 18 to 75 yr, and in BMI from 17.4 to 52.0 kg/m 2 were included in the study. Arm muscle cross-sectional area assessed by anthropometry (AMA caliper ) was compared with mean muscle thickness (MMT) of arm and leg assessed by B-mode US., Results: MMT correlated stronger with TBER than AMA, and reduced the standard error of the estimate (SEE) by 15% in men and by 26% in women. Muscularity was overestimated by AMA caliper due to a systematic error directly proportional to subcutaneous fat layer thickness. The gender independent relation between MMT and TBER norm is described by the equation: TBER norm  = 705-75.4⋅MMT (R 2  = 0.85, SEE = 22.3 Ω/m, P < 0.001)., Conclusions: US-based measurement of limb muscularity provides a more precise prediction of TBER norm , in particular in obese subjects, and is recommended as the method of choice., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

Heterogeneous immunoassays such as ELISA have become indispensable in modern bioanalysis, yet translation into point-of-care assays is hindered by their dependence on external calibration and multiple washing and incubation steps. Here, we introduce RAPPID (Ratiometric Plug-and-Play Immunodiagnostics), a mix-and-measure homogeneous immunoassay platform that combines highly specific antibody-based detection with a ratiometric bioluminescent readout. The concept entails analyte-induced complementation of split NanoLuc luciferase fragments, photoconjugated to an antibody sandwich pair via protein G adapters. Introduction of a calibrator luciferase provides a robust ratiometric signal that allows direct in-sample calibration and quantitative measurements in complex media such as blood plasma. We developed RAPPID sensors that allow low-picomolar detection of several protein biomarkers, anti-drug antibodies, therapeutic antibodies, and both SARS-CoV-2 spike protein and anti-SARS-CoV-2 antibodies. With its easy-to-implement standardized workflow, RAPPID provides an attractive, fast, and low-cost alternative to traditional immunoassays, in an academic setting, in clinical laboratories, and for point-of-care applications., (© 2021. The Author(s).)

Background & Aims: Measurement of total body electrical resistance (TBER) to an alternating current is useful to monitor extracellular water (ECW) in patients on hemodialysis (HD). Which current frequency is preferable is subject of ongoing debate. The aim of this study was to quantify the implications of TBER measurements at current frequencies ranging from 0 to 1000 kHz for ECW monitoring in patients on HD., Methods: Bioimpedance spectroscopy measurements were performed in 39 patients on HD using the Body Composition Monitor (BCM, Fresenius Medical Care). TBER data at 5, 50, 200, 500, and 1000 kHz were compared with the extrapolated TBER at 0 kHz (TBER 0 ) assessed by Cole-Cole analysis. Sensitivity of each TBER configuration was evaluated at individual level, by assessment of the smallest ultrafiltration (UF) volume that induced a significant change in TBER, i.e. a change in TBER ≥ 2.7%., Results: TBER precision was very high for all frequencies, with coefficients of variation of 0.25%-0.28%. Baseline TBER decreased with increasing current frequency. TBER was 2.9% lower at 5 kHz (P < 0.001), 11.6% lower at 50 kHz, and up to 22.0% lower at 1000 kHz. This pattern is attributed to a progressive increase in intracellular current conduction at higher frequencies. Sensitivity to volume changes induced by UF also decreased with increasing current frequency. At 0 and 5 kHz, an UF volume ≤ 0.5 L was sufficient to induce a significant increase in TBER in 87% of patients. This decreased to 69% at higher frequencies., Conclusion: ECW monitoring by TBER requires measurement at 5 kHz or less to ensure optimal performance., Competing Interests: Declaration of competing interest All the authors declared that they had no competing interests., (Copyright © 2021 European Society for Clinical Nutrition and Metabolism. Published by Elsevier Ltd. All rights reserved.)

Background: Fluid balance management in hospitalized patients is hampered by the limited sensitivity of currently available tools. The aim of this study was to assess the sensitivity of total body electrical resistance (TBER) measurements for the detection of extracellular volume (ECV) expansion., Methods: TBER and plasma resistivity (ρ plasma ) were measured during a 4-h infusion of NaCl 0.9% at a rate of 500 mL/h in 23 patients undergoing a diagnostic saline infusion test for primary hyperaldosteronism. Extracellular fluid gain (EFG) was defined as infusion volume minus urinary volume., Results: Infusion of 2.0 L NaCl 0.9% was associated with a mean diuresis of 1.1 ± 0.5 L, an EFG of 0.9 ± 0.5 L, a decrease in ρ plasma of 1.1 ± 0.7 Ω·cm or 1.7 ± 1.0% (P < 0.001), and a decline in TBER of 23.2 ± 10.9 Ω or 4.6 ± 2.2% (P < 0.001). At group level, infusion of 80 mL saline was sufficient to induce a statistically significant decline in mean TBER. At personal level, the decline in TBER was significant on 76% of occasions after an EFG of 0.5-0.75 L, and on all occasions after an EFG of 1.0 L or greater., Conclusion: Raw TBER data are very informative for the detection of ECV expansion induced by the infusion of NaCl 0.9%, with a sensitivity at a personal level that is relevant for clinical practice.

Background & Aims: Assessment of tissue hydration by conventional bioelectrical impedance analysis (BIA) has produced conflicting results because of flaws in the algorithms that are used to translate measurements of total body electrical resistance (TBER) into liters of body water. This type of error can be eliminated by a return to the TBER measurement itself, without attempting to convert Ohms into liters of body water. Aims of this study were to quantify tissue hydration based on TBER, to establish TBER normal values (TBER norm ), to improve the prediction of TBER norm values in individual patients, and to evaluate this approach in patients on hemodialysis (HD)., Methods: TBER norm values were obtained in 213 healthy controls and corrected for body height (H-TBER norm ). Inter-individual H-TBER norm variability was reduced by correction for arm muscle cross-sectional area (AMA). Performance of this approach was evaluated in 94 patients on HD., Results: H-TBER norm was inversely related to AMA. Correction for AMA reduced the H-TBER norm standard deviation by 31% in men and 23% in women. When applied to patients on HD, H-TBER changes within subjects were inversely related to ultrafiltration volumes, with a mean R 2 of 0.95 ± 0.04 in men and 0.93 ± 0.07 in women. Clinically significant H-TBER increments occurred after volume reductions of 0.39 ± 0.25 L in men and 0.37 ± 0.18 L in women., Conclusions: TBER measurements, corrected for height and AMA, have the potential to become an objective and sensitive method to assess hydration in patients. Its clinical value remains to be shown in intervention studies., Competing Interests: Declaration of Competing Interest All the authors declared that they had no competing interests., (Copyright © 2019 European Society for Clinical Nutrition and Metabolism. Published by Elsevier Ltd. All rights reserved.)

Bio-electrical impedance analysis (BIA) is frequently used to assess body composition in man. Its accuracy in patients is limited, possibly because the employed algorithms are based on the assumption that total body electrical resistance (TBER) is exclusively related to body water volume, and that variation in fluid composition and its effect on fluid resistivity can be ignored. This may introduce substantial calculation errors. The aim of this study was to develop an objective method to assess plasma resistivity (ρ plasma ) based on measurements by a conductivity probe, as a surrogate for extracellular fluid resistivity (ρ e ). Sample measurements were standardized at body temperature. Analytical variation was 0.6% within runs and 0.9% between runs. The critical difference, i.e. the smallest difference needed to consider changes within individuals significant, was 1.8% for measurements within runs and 4.3% for measurements between runs. The normal range was defined by a mean ± SD of 66.9 ± 1.8 Ω cm. Multiple regression demonstrated that ρ plasma was inversely related to plasma sodium and chloride concentrations, and positively related to total protein (overall R 2  = 0.92, p < 0.001). In conclusion, ρ plasma measurements were sufficiently robust to be useful as a tool to examine and improve the validity of BIA in clinical settings.

Background: Pharmacokinetic data suggest that the risk of metformin-associated lactic acidosis (MALA) may be increased after Roux-en-Y gastric bypass (RYGB) surgery. The aim of this study was to examine the impact of metformin on plasma lactate levels before and after RYGB surgery., Methods: Retrospective study of plasma lactate levels before and 3 months after RYGB surgery in patients with type 2 diabetes mellitus (T2DM) not using metformin (MET-0, N = 58), on a stable dose (MET-S, N = 138), or on a decreasing dose (MET-D, N = 85) of metformin., Results: Preoperatively, lactate levels were similar in patients on metformin (1.8 ± 0.05 mmol/L) and those not on metformin (1.7 ± 0.08 mmol/L), P = 0.21. Three months postoperatively, lactate levels had decreased in all groups (P < 0.001) to 1.3 ± 0.07 (SE), 1.4 ± 0.05, and 1.2 ± 0.05 mmol/l in MET-0, MET-S, and MET-D, respectively. Lactate levels differed between the groups (P = 0.03), with the lowest level in MET-D. The number of patients with hyperlactatemia (lactate > 2 mmol/l) decreased from 31 to 14%, from 22 to 8.6%, and from 26 to 4.7% in MET-S, MET-0, and MET-D, respectively., Conclusion: Mild hyperlactatemia (lactate > 2 mmol/l) is common in morbidly obese patients with T2DM. It is probably related to increase lactate production by adipocytes. Lactate levels decreased after RYGB-induced weight loss, irrespective of the use of metformin. We therefore conclude that there is no need for routinely lowering of the metformin dose after uncomplicated RYGB surgery, as long as normal renal function is preserved.