Development and Performance of an Albumin-Creatinine Ratio Assay on the Afinion AS100 Analyzer

Abstract

Background: Diabetic nephropathy is one of the most serious and most frequent secondary complications of diabetes mellitus, resulting in increased morbidity and mortality rates. Microalbuminuria is the earliest stage of diabetic nephropathy and is characterized by a persistent and significant elevation in urinary albumin excretion. When quantifying urine proteins, creatinine measurements are used to correct for varying diuresis because creatinine is produced at an approximately constant rate. Methods: The Afinion AS100 Analyzer is a compact, benchtop, multiassay analyzer for point-of-care testing. The Afinion ACR assay presented here analyzes both the albumin and creatinine levels in a urine sample simultaneously within a single device. Albumin is quantified using an immunometric membrane flow through assay, using monoclonal antibody-coated membrane and monoclonal antibodies conjugated to colloidal gold. Creatinine is quantified using an enzymatic colorimetric test involving 4 enzymatic steps. At analysis completion, the concentrations of albumin, creatinine, and albumin-creatinine ratio (ACR) are shown on the Afinion AS100 Analyzer display screen. Results: Measurement ranges are 5 to 200 mg/L (albumin) and 16 to 340 mg/dL (creatinine). Both assays are linear over the whole dynamic range. Comparison of Afinion with Siemens DCA2000 and Roche Modular using 95 samples resulted in a linear correlation coefficient (r) of 0.99 for albumin (both methods) and 0.99 and 1.00, respectively, for creatinine. Total imprecision is 5.5% or lower for albumin, 3.8% or lower for creatinine, and 6.0% or lower for ACR. Conclusions: The Afinion ACR assay provides a reliable, precise, and convenient point-of-care method for simultaneous determination of albumin, creatinine, and ACR in 5½ minutes.