8-Hour Radioimmunoassay for Fibrinopeptide A (FPA)

To allow emergency measurements of FPA in patients,a RIA method was developed in which both the extraction of FPA from plasma and the incubation time of the antigen-antibody mixture were substantially reduced. Extraction with an equilibrium dialyzer allowed a recovery of 54.75 + 1.26% of added FPA (20 ng) within 2½ hrs. At an incubation of 2½ hrs the limit of detection was 1.12 ng/ ml, as compared to 0.54 ng/ml for 24-hr incubation. Rabbits were immunized with synthetic FPA coupled to thyroglobulin with the carbodiimide method. The tracer was produced acc. to Nossel(1971). To preventlabel damage for 10 weeks, the purified radioiodinated peptide was rechromatographed using a QAE-A25 Sephadex column. In 24 normals FPA was 1.01+0.45 ng/ml using 24-hr incubation. For FPA levels above 2 ng/ml the results obtained with the 2½-hr and the 24-hr incubation showed excellent agreement(r=0.99).3.3–25.2 ng/ml were found in 7 patients with venous thromboembolism,a sharp drop to 1.6–5.1 ng/ml being observed 10 minutes after50 mg of heparin i. v.2.3~32 ng/ml were found in 15 patients with various disorders(4 malignancy, 4 aorticaneurysm,2 nephropathy, 2 anginal attack, 1septicemia, 1 lung abscess, 1 CVI ) . Values of 3.6–80 ng/ml were found after infusion of a prothrombin complex concentrate in 5 patients with hemophilia B. The method is valuable for the emergency coagulation work-up of patients.