Fibrinogen and Platelets in the Primary Arrest of Bleeding

Abstract Two patients with a congenital absence of fibrinogen and a prolonged bleeding time were studied to determine the role of fibrinogen in the primary arrest of bleeding and for further clarification of the fibrinogen requirement for platelet function. The retention of platelets, sampled directly from venous blood, in glass-bead filters was consistently decreased and was markedly increased by pretreatment of the beads with fibrinogen. Adhesion of platelets to connective tissue, however, was normal. In citrated platelet-rich plasma (PRP), abnormalities in primary platelet aggregation by ADP and epinephrine were optimally corrected by fibrinogen in concentrations of 10 to 20 mg per 100 ml. In contrast to the abnormal findings in citrated PRP, both primary platelet aggregation and the release reaction were normal in heparinized PRP. The studies leave unanswered the question of the fibrinogen requirements for platelet aggregation, but indicate that fibrinogen is required as a cofactor in the interaction ...