Activation systems in contrast idiosyncrasy.

: Both animal and human data suggest the possibility that the C1 esterase inhibitor may play an important controlling role in contrast media systemic reactions. This critical controlling protein has a major inhibitory effect on C1, kallikrein, activated factor XII of the intrinsic coagulation system, and on plasmin. In addition, it probably has other inhibitory effects not so well documented. Any circumstance that contributes to a continuing activation of the complement, coagulation, kinin, or fibrinolytic systems may result in partial consumption of the inhibitor and predispose the individual to adverse reactions to contrast challenge.