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Thrombus-related uptake of 131 I-fibrin des-AABB has been compared to that of 125 I-fibrinogen in 13 patients with established venous thrombosis. Both tracers originated from a common pool of beta-alanine precipitated fibrinogen. Scan-recordings were performed as a radiofibrin (ogen) uptake test. Uptake characteristics of des-AABB fibrin were similar to those of fibrinogen, when measured as percentage of concomitant radioactivity over the heart. Due to its longer circulation time, fibrinogen was superior to fibrin des-AABB for the detection of venous thrombi. Circulating des-AABB fibrin was cleared biphasically, with an initial rapid decline followed by a gradual exponential decrease. Mean half-lives were 5.5 +/- SD 3.5 hr and 10 +/- SD 3.5 hr, respectively. The elimination rates were uninfluenced by thrombus activity, as judged by the fibrin(ogen) uptake test. Metabolic half-life of fibrinogen in the total material was 62 +/- SD 19 hr. Dissociation of fibrinogen and soluble des-AABB fibrin clearance rates was evident, describing their own, independent elimination patterns, probably reflecting different clearing mechanisms.

The serum and urine concentrations of fibrin/fibrinogen degradation products (F.D.P.) were estimated in 172 patients with glomerulonephritis. In each case the diagnosis was established on the basis of clinical, renal histological, and ultrastructural findings. Serum F.D.P. concentrations were often raised in all types of glomerulonephritis, though more consistently in active proliferative forms. The urinary concentration provided a reliable and sensitive index of activity, progression, and natural history in proliferative glomerulonephritis. In these forms the urinary F.D.P. content was thought to reflect predominantly lysis of intraglomerular fibrin deposits. In minimal lesion and membranous glomerulonephritis low but abnormal concentrations of urinary F.D.P. were consistently found. It is suggested that in these cases the products are derived from limited proteolysis of fibrinogen filtered through an abnormally permeable basement membrane.Daily measurement of urinary F.D.P. concentration is of potential value in the differential diagnosis of patients with glomerulonephritis and at the same time provides a sensitive assessment of the activity and natural history of proliferative disease.