Cyanide-Nitroprusside Colorimetric Assay: A Rapid Colorimetric Screen for Urinary Cystine.

Background: Cystinuria is an autosomal recessive disorder resulting in poor proximal tubule reabsorption of cystine in the nephron, increasing the risk of cystine stone formation. A fast, inexpensive assay to screen for urinary cystine is needed because cystine stones are difficult to noninvasively differentiate from more common calcium-containing ones. Tandem mass spectrometry (MS/MS) is sensitive and specific but is labor-intensive and costly.

Creatinine-Based and Cystatin C-Based GFR Estimating Equations and Their Non-GFR Determinants in Kidney Transplant Recipients.

Background And Objectives: eGFR equations have been evaluated in kidney transplant recipients with variable performance. We assessed the performance of the Modification of Diet in Renal Disease equation and the Chronic Kidney Disease Epidemiology Collaboration equations on the basis of creatinine, cystatin C, and both (eGFR creatinine-cystatin C) compared with measured GFR by iothalamate clearance and evaluated their non-GFR determinants and associations across 15 cardiovascular risk factors.

Design, Setting, Participants, & Measurements: A cross-sectional cohort of 1139 kidney transplant recipients >1 year after transplant was analyzed.

Performance of cystatin C- and creatinine-based estimated glomerular filtration rate equations depends on patient characteristics.

Background: The Kidney Disease Improving Global Outcomes (KDIGO) guideline recommends use of a cystatin C-based estimated glomerular filtration rate (eGFR) to confirm creatinine-based eGFR between 45 and 59 mL · min(-1) · (1.73 m(2))(-1). Prior studies have demonstrated that comorbidities such as solid-organ transplant strongly influence the relationship between measured GFR, creatinine, and cystatin C.

Fecal electrolyte testing for evaluation of unexplained diarrhea: Validation of body fluid test accuracy in the absence of a reference method.

Background: Validation of tests performed on body fluids other than blood or urine can be challenging due to the lack of a reference method to confirm accuracy. The aim of this study was to evaluate alternate assessments of accuracy that laboratories can rely on to validate body fluid tests in the absence of a reference method using the example of sodium (Na(+)), potassium (K(+)), and magnesium (Mg(2+)) testing in stool fluid.

Methods: Validations of fecal Na(+), K(+), and Mg(2+) were performed on the Roche cobas 6000 c501 (Roche Diagnostics) using residual stool specimens submitted for clinical testing.

Serum cystatin C predicts vancomycin trough levels better than serum creatinine in hospitalized patients: a cohort study.

Introduction: Serum cystatin C can improve glomerular filtration rate (GFR) estimation over creatinine alone, but whether this translates into clinically relevant improvements in drug dosing is unclear.

Methods: This prospective cohort study enrolled adults receiving scheduled intravenous vancomycin while hospitalized at the Mayo Clinic in 2012. Vancomycin dosing was based on weight, serum creatinine with the Cockcroft-Gault equation, and clinical judgment.

Oxalate quantification in hemodialysate to assess dialysis adequacy for primary hyperoxaluria.

Background: Patients with primary hyperoxaluria (PH) overproduce oxalate which is eliminated via the kidneys. If end-stage kidney disease develops they are at high risk for systemic oxalosis, unless adequate oxalate is removed during hemodialysis (HD) to equal or exceed ongoing oxalate production. The purpose of this study was to validate a method to measure oxalate removal in this unique group of dialysis patients.

Urine but not serum soluble urokinase receptor (suPAR) may identify cases of recurrent FSGS in kidney transplant candidates.

Background: Recently, serum soluble urokinase receptor (suPAR) has been proposed as a cause of two thirds of cases of focal segmental glomerulosclerosis (FSGS). It was noted to be uniquely elevated in cases of primary FSGS, with higher levels noted in cases that recurred after transplantation. It is also suggested as a possible target and marker of therapy.

Measurement of urinary TGF-β1 in patients with diabetes mellitus and normal controls.

Objective: Increasing evidence links TGF-β1 to progression of renal fibrosis including its association with diabetic nephropathy (DN). Current ELISA assays are not sensitive enough to measure TGF-β1 in the urine of many clinically healthy individuals, even those with established renal disease. The objective of this study was to validate a sensitive urinary assay for TGF-β1 and compare levels between healthy controls and patients with established DN.

Analytic and clinical validation of a standardized cystatin C particle enhanced turbidimetric assay (PETIA) to estimate glomerular filtration rate.

Background: Cystatin C is an alternative biomarker for assessing glomerular filtration rate (GFR), yet lack of standardization could hinder its widespread use. In this study we analytically and clinically validated a newer cystatin C particle-enhanced turbidimetric assay (PETIA) traceable to a certified reference material and compared it to the more commonly used particle-enhanced nephelometric assay (PENIA).

Methods: Samples from four patient cohorts at the Mayo Clinic were studied: 1) clinical convenience samples (n=50); 2) samples from patients undergoing iothalamate urinary clearance testing for clinical indications (n=101); 3) volunteers without kidney disease (n=292); 4) samples from 1999-2000 with previous cystatin C measurements.

Assessment of clinical performance without adequate analytical validation: A prescription for confusion.

Objectives: Lp-PLA2 is a biomarker with promise for predicting cardiac risk. The lack of reproducible results has limited its use. In evaluating a new reagent kit, we investigated conditions for optimal reproducibility.