The effect of incubation at 4 degrees C upon the one stage prothrombin times and the Thrombotest times of plasma from normal people, females taking oral contraceptive agents (O.C.A.’s) or in the third trimester of pregnancy, and patients with hereditary angioneurotic edema (H.A.N.E.) was measured to determine if enhancement of coagulant activity was regularly associated with reduced amounts of C1(-)- inhibitor (C1(-)-INH) in the plasma. Cold-enhanced coagulant activity was not always found in H.A.N.E. plasmas, markedly deficient in C1(-)- INH, and when found, the addition of purified C1(-)-INH to the plasma did not always prevent its development in vitro. Females taking O.C.A.’s regularly demonstrated cold-enhanced plasma coagulant activity in this series, as did pregnant females tested, as reported by others. The relation of C1(-)-INH levels in plasma to the cold-enhanced plasma coagulant activity was imperfect. In plasma obtained during pregnancy, but not exposed to 4 degrees C, C1(-)-INH levels were low despite minimal shortening of the Thrombotest time. Thus, these observations suggest that reduced levels of C1(-)-INH in plasma was not directly related to the tendency to generate enhanced coagulant activity at 4 degrees C. Other factors must be critical to the development of this activity, and the failure to block its development in C1(-)-INH deficient plasmas by adding purified C1(-)-INH at venesection suggests that events which initiate the development of this property may have occurred in vivo.
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