Summary
1. Our experiments demonstrate that antithrombin I interferes considerably in the thrombin inhibitor determination described by Jürgens. A similar interference can be suspected in the immediate antithrombin determinations as described by other investigators in experiments based on the same principle.
2. The thrombin-adsorbing capacity of fibrin depends to a high degree on the ionic strength of the medium: low ionic strength enhances, while high concentrations inhibite antithrombin J activity.
3. After allowing for antithrombin I interference in the total thrombin inhibition, there was still measurable direct antithrombin activity present. The magnitude of the latter is directly correlated to the antithrombin capacity found in plasma samples free of the antithrombin I side-effect. Such plasma samples were obtained from a patient with congenital afibrinogenemia and heat-defibrinated normal plasma.
