How to measure small amounts of protein in dog urine accurately

Abstract

BACKGROUND: The presence of albumin in urine, even in small amounts, is always abnormal and usually reflects kidney dysfunction. Different techniques are commercially available for the measurement of microalbuminuria in dogs. OBJECTIVES: The purpose of this study was to compare the accuracy of semiquantitative test strips, urine protein electrophoresis, and a validated immunoturbidimetric assay in the measurement of microalbuminuria in dogs. METHODS: Urine samples were collected from 307 dogs presented to The Queen's Veterinary School Hospital, University of Cambridge, for a variety of clinical conditions. Urine was collected by midstream free catch (193/307, 63%), cystocentesis (89/307, 29%), or catheterization (25/307, 8%). Routine urinalysis was performed on all samples. Albumin was measured by using semiquantitative test strips, by agarose gel electrophoresis, and by an automated immunoturbidimetric assay designed for human samples (considered as the gold standard). The latter was validated using a purified canine albumin standard. RESULTS: The immunoturbidimetric assay had within-assay and between-assay coefficients of variation (CV) of 1.3% and 5.0%, respectively, overall recovery of 97.1%, and high linearity (r=.985). Of the samples with measurable albumin (>1.4 mg/L) by the immunoturbidimetric assay, 57/195 (29%) were negative for albumin using the semiquantitative test strips and 138/195 (71%) were positive. Urine protein electrophoresis (UPE) and immunoturbidimetric results had a concordance CV of 86%. CONCLUSIONS: UPE and semiquantitative test strips are less accurate than the automated immunoturbidimetric method for the measurement of albumin in canine urine.