Platelet Antithrombin Deficiency: A New Clinical Entity

A kindred with a history of multiple thromboses was studied for coagulant abnormalities. A deficiency of plasma antithrombin III was found in approximately half of the 13 family members by either coagulant or immunologic assay. No clear relationship between plasma antithrombin III deficiency and a history of thrombosis was present. Platelet antithrombin assays were studied in the same family. Ten of the 13 members were deficient. None of the three who was normal had a history of thrombosis. The plasma antithrombin III assays could be influenced by heparin or coumarin treatment. The same medications were without consistent effect on platelet antithrombin. On the basis of these findings, it is proposed that familial hypercoagulability in some cases may be due to a platelet antithrombin deficiency and that the plasma antithrombin III deficiency is a secondary effect.