Radioimmunoassay for immunologlobulin G in serum and urine

We describe a radioimmunoassay for immunoglobulin G (IgG) in serum and urine. Aliquots of diluted samples and 125I-labeled IgG were incubated in antibody-coated tubes at 37 degrees C for 24 h, the supernates were decanted, and the radioactivity in tubes containing the bound fraction was counted. The dose-response curve in the range of 0.4--500 mg/L of urine or 640--40 000 mg/L of serum was linear on logit-log transformation and iterative weighted regression. Assay sensitivity was 10 ng of IgG. Validation studies included testing for precision, accuracy, antibody specificity, and parallelism of the dose-response curves for standard and unknown. In a study of 14 apparently normal individuals, serum IgG = 4.0-10.9 gL, urine IgG = 1.1-4.8 mg/24 h, and IgG clearance = 0.2 X 10(-4) to 4.8 X 10(-4) mL/min. In 20 patients with renal allografts, serum IgG = 15.8-66 g/L, urine IgG - 9.6-626 mg/24 h, and IgG clearance = 9 X 10(-4) to 1.99 X 10(-1) mL/min. IgG values correlated well with severity of renal allograft rejection.