Increased prothrombin activation in a patient with congenital afibrinogenemia is reversible by fibrinogen substitution.

We describe a patient with congenital afibrinogenemia who showed elevated prothrombin activation fragments (F1 + 2) indicating increased thrombin formation. This finding was unexpected since it has hitherto been thought that patients with congenital hypo- or afibrinogenemia have no evidence of increased utilization or accelerated consumption of coagulation factors. No other possible reasons for the elevation of F 1 + 2 were found. Upon fibrinogen substitution F1 + 2 decreased and were again increasing when fibrinogen concentration in plasma fell to very low levels. These findings raise the question of whether increased thrombin formation should be understood as a compensatory mechanism in congenital afibrinogenemia.