Urine Albumin-to-Creatinine Ratio

Abstract

The evaluation of urinary protein is a cornerstone for the diagnosis and treatment of kidney disease. Quantification of proteinuria is used to inform fundamental clinical decisions, such as whether to refer to a nephrologist, perform a kidney biopsy, or initiate therapy. Furthermore, minute interindividual differences in proteinuria associate with future risks for heart disease, kidney failure, and cancer in general population studies.1–3 These findings motivate optimal and consistent methods to quantify proteinuria in the clinical setting. In this issue of JASN , Heerspink et al. 4 compare, among 701 participants in the Reduction In Endpoints in Noninsulin Dependent Diabetes Mellitus with the Angiotensin-II Antagonist Losartan (RENAAL) trial, four standard methods for measuring urine protein: 24-hour urine protein excretion, 24-hour urine albumin excretion, first morning void spot urine albumin concentration, and first morning void spot urine albumin-to-creatinine ratio (ACR). Unlike most previous studies, which related spot urine albumin or urine protein measurements to the gold standard, 24-hour urine collection, the study by Heerspink et al. 4 addresses which of the four methods most strongly associates with the clinical outcome of …