Summary
Prolonged prothrombin time was measured in four haemophilia B patients with the aid
of bovine or rat thromboplastins, whereas normal values were obtained when human or
rabbit thromboplastin was used. The anomaly can be ascribed to the decreased level
of factor VII. Four carrier relatives exhibited normal prothrombin time independent
of the source of thromboplastin. The prolonged prothrombin time appears to be a non-hereditary
phenomenon and it may be attributed to a species- specific interaction between thromboplastin
of diverse sources and human factor VII, rather than to anomalous factor IX.
