COMPARISON OF URINE DIPSTICKS WITH QUANTITATIVE METHODS FOR MICROALBUMINURIA

We describe a new dip-and read dipstick that detects urine albumin at concentrations of 10 mg/l and above and urine creatinine at concentrat ions of 300 mg/l and above. The albumin assay is based on a high-affin ity, dye-binding technique while the creatinine assay is based on the peroxidase-like activity of copper creatinine complexes. With these tw o-test dipsticks, urines from normal adults supplemented with albumin and creatinine were correctly identified to within +/-15% of the expec ted value for both analytes; the between-day coefficients of variation ranged from 7.1% to 16.1%. We tested 275 patients' unmodified urines by the Bayer and Boehringer Mannheim Micral-Test(R) albumin dipsticks and for albumin with the Beekman Array on the same specimens. We also analyzed 42 selected urines from the group of 275 for albumin by anoth er quantitative immunochemical method and by electrophoresis plus a to tal protein method to estimate the albumin concentration. The quantita tive immunochemical methods appear to underestimate the urine albumin concentrations; in these 42 urines measured as negative, i.e., <ca. 16 -20 mg/l, by one of the quantitative method but positive by the Bayer dipstick, 33 of these were positive by the electrophoresis/total prote in assay combination. The Bayer albumin dipstick correctly identified urines as having <16 mg/l or greater than or equal to 16 mg/l at an 80 % rate. At a cutoff of 20 mg/l, the rate increased to 87%. We also det ermined the urinary albumin/creatinine ratios on the 275 patients usin g the Bayer two-pad dipstick and found agreement 84% of the time with the same ratio obtained from a quantitative immunochemical method for albumin and a rate-Jaffe method for creatinine; an albumin/creatinine ratio (mg/g) of 30 was used as the discrimination point. Albumin stabi lity studies performed on the Beekman Array patients with six fresh ur ines showed small but consistent decreases at -20 degrees C but not at 4 degrees C after one month of storage. The albumin in contrived urin es, as estimated by electrophoreses/total protein and by the dipsticks did not change at these storage conditions. Boric acid at 1 g/l as a urine preservative had no effect on the measurement of albumin by any of the methods described here nor of the assay of creatinine. Other ur inary proteins present at abnormal excretion rates did not interfere w ith the Bayer albumin dipstick. Abnormal concentrations of bilirubin, citrate, creatine, ascorbic acid, albumin, hemoglobin and myoglobin in urine did not interfere with the creatinine dipstick measurements. Th e first four of the above did not affect the Bayer dipstick results fo r albumin.