Radioimmunoassay for Urinaryalbumin Materials and Methods

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 1251.. labeled albumin and a rabbit antiserum monospecific for human albumin. Phase separation was effected by the double-antibody tethnique. 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 UaIb was 2.2-12.6 mg/24 h, and for albumin clearance (C8lb), 1.8 X 10-19.6 X iO mI/mm. After renal homografts in 25 patients, UaIb ranged from 16.9 to 9928 mg/24 h, and CaIb from 2.7 X i0 to 1.7 X 10-1 mI/mm. Both increased Ualb and Caib correlated well with the severity of renal homograft rejection.