RAPID SCREENING OF LOW-MOLECULAR-MASS PROTEINURIA - EVALUATION OF THE 1ST IMMUNOCHEMICAL TEST STRIP FOR THE DETECTION OF ALPHA(1)-MICROGLOBULIN IN URINE

A new semiquantitative immunochemical test strip for urinary alpha1-microglobulin, a marker protein for tubular proteinuria, was assessed. This test strip has four colour zones, reflecting alpha1-microglobulin concentrations of ca. 10, 25, 50, and 80 mg/l. Alpha1-Microglobulin concentrations were measured by means of the test strip and an immunonephelometric 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 misclassification of over 70% of the results. Correlation between both methods was highly significant, with a Spearman rank correlation coefficient of r(s) = 0.84 (P < 0.001). There was a partial overlap of the test strip results in different concentration ranges. An elevation of alpha1-microglobulin was defined as > 25 mg/l, calculated as the upper limit of the central 95% interval of alpha1-microglobulin concentration in urine samples measured in a previous study of 304 healthy adults. Using this definition of alpha1-microglobulin 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 alpha1-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.