Congenital Idiopathic Hypoprothrombinemia1

Summary Attention is drawn to the fact that a prolongation of the prothrombin time existing from birth may be due to a decrease of prothrombin, to a decrease of the recently described prothrombin conversion factors, and to a combination of both. Therefore, apart from true hypoprothrombinemia, pseudo‐hypo‐prothrombinemia must be distinguished. These advances in our knowledge make it necessary to reconsider cases earlier indicated as congenital idiopathic hypoprothrombinemia. A family with true congenital idiopathic, hypoprothrombinemia is described in detail. With the plasma of one of the members of this family the problem of the formation of thromboplastin was studied.