Characterization and significance of urinary fibrin degradation products

Urine samples from patients with renal disease and proteinuria were examined for material which reacted with antisera to fibrinogen or its degradation products (FDP). Such material was found in samples from 9 of 24 patients and was characterized in 8 patients by immunodiffusion in agar gel, immunoelectrophoresis in cellulose acetate, electrophoresis in acrylamide gel with subsequent immunodiffusion in agar gel, and/or gel filtration with Sephadex G-200. All 8 urine samples contained FDP while none contained thrombin-clottable fibrinogen. The FDP were of early, late, and intermediate types in 5 samples, early and intermediate in 2 samples, and only late in 1 sample. Selectivity of proteinuria according to molecular size was determined in 9 patients by gel filtration (Sephadex G-200) of urine and serum samples. Six of these patients had urinary FDP. The presence or absence of fibrin, fibrinogen, or FDP within glomeruli was ascertained by immunofluorescent observation of renal biopsies from 22 patients. Urinary FDP appeared to be related to nonselectivity of proteinuria rather than to the presence of fibrinogen or its derivatives within glomeruli. Both low selectivity and urinary FDP were found only in patients with severe proliferative and exudative glomerular lesions. Furthermore, improvement of the clinical course in 2 patients following initiation of steroid treatment was accompanied by increased selectivity of proteinuria and disappearance of urinary FDP.