Radioimmunoassay for urinary albumin.

We describe a rapid, sensitive, and precise radioimmunoassay for urinary albumin (Ualb). 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 as linear in the range of 15.6-10000 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 Ualb was 2.2--12.6 mg/24h, and for albumin clearance (Calb, 1.8 x 10(-5)-19.6 x 10(-5) ml/min. After renal homografts in 25 patients, Ualb ranged from 16.9 to 9928 mg/24 h, and Calb from 2.7 x 10(-4) to 1.7 x 10(-1) ml/min. Both increased Ualb and Calb correlated well with the severity of renal homograft rejection.