Radioimmunoassay for urinary albumin

Abstract

Described is a rapid, sensitive, and precise radioimmunoassay for urinary albumin (U(alb)). Aliquots of diluted urine were incubated at room temperature for 1 h with 125I-labeled albumin and a rabbit antiserum monospecific for human albumin. Phase separation was effected by the double-antibody technique. The dose-response curve was linear in the range of 15.6 - 10,000 ng, equivalent to 4 to 3000 mg/liter of urine. The limit of sensitivity was 16 ng of albumin. The coefficient of assay variation was 4.8%, both at 44 mg/liter and at 1304 mg/liter. A displacement curve obtained with a serially diluted urine sample of high albumin concentration was completely superimposable with the curve for which human albumin was used as a standard. In 26 normal individuals the range for U(alb) was 2.2 - 12.6 mg/24 h, and for albumin clearance (C(alb)), 1.8 x 10-5 - 19.6 x 10-5 ml/min. After renal homografts in 25 patiets, U(alb) ranged from 16.9 to 9928 mg/24 h, and C(alb) from 2.7 x 10-4 to 1.7 x 10-1 ml/min. Both increased U(alb) and C(alb) correlated well with the severity of renal homograft rejection.