Inhibition of cold-promoted activation of the prothrombin time studies of new siliconized borosilicate collection tubes in normals and patients receiving warfarin.

Studies of the prothrombin time in normals and patients receiving oral anticoagulant therapy revealed a partial inhibition of the in vitro cold-promoted activation of Factor VII and shortening of the prothrombin time when blood was collected in a new commercial siliconized borosilicate tube (Becton-Dickinson, Rutherford, NJ, 6418 and 6419). The data collected with normal blood indicated that the cold-promoted activation was almost totally inhibited, while the patients had only a mean reduction of 50% of the cold-promoted activation. In pregnant patients there was no inhibition of the cold-promoted activation of the prothrombin time or Factor VII using the new siliconized tubes.