Factor VII in plasma of women taking oral contraceptives. Lack of cold activation under blood bank conditions.

Factor VII in plasma from about 15 percent of healthy subjects undergoes activation when samples are kept in plastic tubes at 4 degrees C. In women taking oral contraceptives, this phenomenon is observed much more frequently. If this phenomenon occurred under blood bank conditions as well, the transfusion of such plasma from donors taking oral contraceptives to patients afflicted by trauma could enhance thromboembolism. Plasma packs of 72 female donors taking oral contraceptives were separated and stored at 4 degrees C for 24 hours in the blood bank. No significant change in factor VII:C level was observed: The initial level was 110.2 +/- 6.2 U per dl (mean +/- SEM), and the 24-hour level, 97 +/- 3.3 U per dl. Among the 72 donors, 10 were identified as cold activators; their factor VII:C level increased from 85.6 +/- 2.5 U per dl (mean +/- SEM) to 222.0 +/- 7.5 U per dl when their plasma samples were kept in plastic tubes for 24 hours at 4 degrees C. In contrast, the factor VII:C level in the plasma packs kept simultaneously in the blood bank at 4 degrees C was only 101.1 +/- 9.0 U per dl at 24 hours. Thus, it appears that plasma from donors taking oral contraceptives can be used safely even when they are not frozen immediately.