A new observation of a hemorrhagic diathesis associated with the presence of an anticoagulant in the circulating blood is reported here. The patient was a 21 year old male, appearing by clinical evaluation to have hemophilia, but without a family history of hemophilia. The blood and plasma were strongly anticlotting and had a very long clotting time. The clotting time of recalcified citrated plasma was greatly delayed by removing the platelets. Freezing and thawing of platelet-rich plasma resulted in a marked shortening of the clotting time. Dilution of the plasma shortened the clotting time, while the addition of calcium and storage of the plasma had no effect.

The prolonged clotting time was not corrected by the addition of normal plasma or plasma fractions having antihemophilic activity. The prothrombin time was nearly normal. Small quantities of thromboplastin were very effective in shortening the clotting time. The anticoagulant had no antithrombin activity. The "progressive" antithrombin and antifibrinolysin of the patient’s plasma were normal.

The anticoagulant acts during the first phase of coagulation by inhibiting an (plasma) activator of prothrombin. It appears to be identical with the anticoagulant described in three previous publications from the United States.

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