ALBUMIN DETERMINATION IN FROZEN URINES - UNDERESTIMATED RESULTS

Albumin determination by radioimmunossay in fresh and frozen urine collections from 73 patients were performed. The values for albumin in fresh urines were 1-200 mg/24 h and were significantly higher (p < 0.001) than the corresponding values in urines frozen for seven days (40.7 mg/24 h .+-. 5.0 vs. 32.0 mg/24 h .+-. 4.3.) Similar results were obtained for protein determination, using turbidimetry, in urine specimens was higher (p < 0.001) in the pellets from frozen urines compared to urines kept at 4.degree. C for 1 and/or 7 days. By contrast, the radioactivity in the pellet of fresh urines kept at 4.degree. C for 1 and/or 7 days did not show any significant change. We suggest that freezing results in a partical albumin and protein sedimentation. Thus, determination of albumin in frozen urine specimens underestimates the real value by about 20%. This underestimation will limit our ability to diagnose borderline cases of microalbuminuria.