Urinary excretion of C3 antigen in glomerulonephritis.

C3 and fibrin degradation products (F.D.P.) have been measured in early morning urine samples from 38 normal people and 123 patients with glomerulonephritis. Normal urine contained less than 0.3 mug of either antigen per ml. C3 and F.D.P. were both detected in the urine of many patients with glomerulonephritis. Levels above 1 mug/ml were exceptional in patients with "minimal change," and the highest excretion of both antigens occurred in mesangiocapillary glomerulonephritis, membranous nephropathy, and focal glomerulosclerosis.Both C3 and F.D.P. excretion showed considerable variation with time, with parellel fluctuations in the two antigens. These fluctuations did not depend on the total protein leakage and suggest that the complement and clotting sequence are closely related in these glomerular disorders.