RAPID SCREENING OF LOW-MOLECULAR-MASS PROTEINURIA - EVALUATION OF THE1ST IMMUNOCHEMICAL TEST STRIP FOR THE DETECTION OF ALPHA(1)-MICROGLOBULIN IN URINE

A new semiquantitative immunochemical test strip for urinary alpha1-mi croglobulin, a marker protein for tubular proteinuria, was assessed. T his test strip has four colour zones, reflecting alpha1-microglobulin concentrations of ca. 10, 25, 50, and 80 mg/l. Alpha1-Microglobulin co ncentrations were measured by means of the test strip and an immunonep helometric method in 330 samples collected as the second voided mornin g 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 inst ructions led to misclassification of over 70% of the results. Correlat ion between both methods was highly significant, with a Spearman rank correlation coefficient of r(s) = 0.84 (P < 0.001). There was a partia l overlap of the test strip results in different concentration ranges. An elevation of alpha1-microglobulin was defined as > 25 mg/l, calcul ated as the upper limit of the central 95% interval of alpha1-microglo bulin concentration in urine samples measured in a previous study of 3 04 healthy adults. Using this definition of alpha1-microglobulin eleva tion, a sensitivity of 97.5%, specificity of 73.6%, a false-positive r ate of 16.6%, and a false-negative rate of 0.9% of the test strip resu lts were obtained. A fraction of 82.4% of the 330 samples investigated was correctly classified as having increased alpha1-microglobulin con centration or not. Methodical improvements of the test strip are neces sary to reduce overlapping results, in order to make the test suitable for screening purposes.