Polycythaemia vera and Christmas disease with slightly prolonged prothrombin time.

A family is reported in which Christmas disease in one member and polycythaemia in another were associated with prolongations of the one-stage prothrombin time of the factor-VII deficiency type. Changes in the prothrombin time were present in the siblings of the case of Christmas disease and in a number of unrelated cases of polycythaemia vera. The use of "mixing procedures" did not reveal any significant mutual correction of the changes in prothrombin time.