Rapid Screening of Low Molecular Mass Proteinuria: Evaluation of the First Immunochemical Test Strip for the Detection of α1-Microglobulin in Urine

Summary: A new semiquantitative immunochemical test strip for urinary armicroglobulin, a marker protein for tubular proteinuria, was assessed. This test strip has four colour zones, reflecting armicroglobulin concentrations of ca. 10, 25, 50, and 80 mg/1. otrMicroglobulin concentrations were measured by means of the test strip and an immunonephelo metric method in 330 samples collected as the second voided morning urine. The reading time of the test strip must be strictly observed. Reading one minute earlier or later than the 5 min stated in the instructions led to misclassifica tion of over 70% of the results. Correlation between both methods was highly significant, with a Spearman rank correlation coefficient of rs = 0.84 (P 25 mg/1, calculated as the upper limit of the central 95% interval of a,microglobulin concentration in urine samples measured in a previous study of 304 healthy adults. Using this definition of ocrmicroglobulin elevation, a sensitivity of 97.5%, specificity of 73.6%, a false-positive rate of 16.6%, and a false-negative rate of 0.9% of the test strip results were obtained. A fraction of 82.4% of the 330 samples investigated was correctly classified as having increased oci-microglobulin concentration or not. Methodical improvements of the test strip are necessary to reduce overlapping results, in order to make the test suitable for screening purposes.