To evaluate the advantages and drawbacks of six commercially available techniques in the measurement of microalbuminuria in diabetic patients.
Timed overnight urine samples from 75 patients in our diabetic clinic were tested with 2 qualitative tests (Micral-Test and Microbumintest) and assayed with 4 quantitative tests, which used different methodologies: double-antibody RIA, RID, IT, and NEPH. All tests were commercially available. The double-antibody RIA was taken as the golden standard. All urine samples were either negative or trace by Albustix (Ames, Elkhart, IN). Interobserver variation for the 2 qualitative tests was assessed by asking 12 experienced nurses to read the color changes on the dipsticks and the tablets simultaneously, using test solutions with albumin concentrations of 16, 32, and 64 mg/L.
The 75 urine samples contained 0–154.2 mg/L of albumin. Correlation coefficients of RID, NEPH, and IT with RIA were 0.970, 0.975, and 0.974, respectively. Intra-assay and interassay CVs ranged from 1.36–11.5%. Microbumintest had a higher sensitivity (100 vs. 75%), but lower specificity (82.5 vs. 87.3%) than Micral-Test. Considerable interobserver variation existed in the matching of colors for both tests. Discrepancies were especially significant with Microbumintest, with 8 of 12 nurses misreading the 32 mg/L level.
Correlations of the 3 quantitative methods with RIA were all >0.970. Choice of test may depend more on considerations such as time, space, number of specimens to be handled, and availability of instruments. Both qualitative tests showed a relatively low specificity. Positive tests must be confirmed with quantitative assays before microalbuminuria is diagnosed. Microbumintest had a higher sensitivity, but its unacceptably high interobserver variation and lower specificity were serious drawbacks.