Albumin is the most commonly identified protein in the urine. This study compared the diagnostic performance of the urine dipstick colorimetric test, sulfosalicylic acid (SSA) turbidimetric test, and urine protein–creatinine (UPC) ratio in identifying albumin. A species-specific enzyme-linked immunosorbent assay (ELISA) for urine albumin was used as the reference point. The urine tested was from healthy dogs (N = 559) and cats (N = 347). Results for urine dipstick and SSA tests were considered positive when trace protein was detected; the tests had a specificity of 81.2% and 73.3%, respectively, and a poor predictive value (34% and 41.8%, respectively) in dogs. Increasing the cutoff to ≥ 2+ for the dipstick and SSA tests increased specificity to > 90% for both tests. In cats, dipstick and SSA tests had very poor specificity (11% and 25.4%, respectively), and poor positive predictive value (55.6% for dipstick; 46.9% for SSA). Increasing the cutoff to ≥ 2+ in cats improved both tests’ specificity (80% for dipstick; 94.2% for SSA) and positive predictive value (63.5% for dipstick; 65.2% for SSA). The UPC ratio had a high specificity for albuminuria in dogs and cats (99.7% in dogs; 99.2% in cats) but low sensitivity (28.7% in dogs; 2% in cats). Based on these findings, the authors recommended that if trace protein is identified on a urine sample in dogs, it should be confirmed with a SSA test; results of both tests should be positive to consider the results “positive for albumin.” There is a high probability of disease when the urine dipstick or SSA test result is positive with a result of ≥ 2+. Both urine dipstick and SSA tests were considered to be of minimal diagnostic value in cats due to the large number of false-positive results, and the UPC ratio had an unacceptable number of false-negative results. In cats, urine albumin is best determined by a species-specific ELISA. Study supported by HESKA

Commentary: The urine dipstick provides a fast, easy, and reliable method for detecting albuminuria. Confirmatory and quantitative test methodologies can present interpretive challenges, as results obtained from varied platforms may seem conflicting to those unfamiliar with analytic intricacies. This article provides an excellent comparison of 3 methods frequently used to detect albuminuria in normal dogs and cats while using a fourth method (species-specific ELISA) as the “gold standard.” Those who routinely perform and interpret urine protein assessments are furnished with validation that dipstick detection of albuminuria at lower albumin or protein concentrations from a single sample is of poor diagnostic value.—Carolyn A. Sink, MS, MT

Comparison of urine dipstick, sulfosalicylic acid, urine protein to creatinine ratio, and species specific ELISA methods for detection of albumin in the urine samples of cats and dogs. Lyon SD, Sanderson MW, Vaden SL, et al. JAVMA 236:874-879, 2010.