Fibrinopeptide A immunoreactivity in human plasma.

Abstract A radioimmunoassay was developed for the determination of human fibrinopeptide A (fpA) in plasma. The detection limit of the assay was 0.5 ng/ml. Only fibrinogen and fibrinogen derivatives containing the fpA-moiety cross-reacted strongly in the assay, necessitating dialysis of plasma prior to the determination of its fpa level. The recovery of fpA added to plasma was 25% after dialysis. In normal plasma fpA-immunoreactivity equivalent to 0.4–2.4 ng per ml was found (mean ± 2 SD, not corrected for loss during dialysis, n=37). Increased levels of fpA-immunoreactivity were found in some patients with deep vein thrombosis or low grade intravascular coagulation. During hypertonic saline induced abortion the rise of fpA-immunoreactivity preceded the appearance of fibrin monomers and fibrin degradation products. The method is very sensitive for the detection of thrombin activity in vitro.