Complement activation following intravenous contrast material administration.

Untoward reactions to iodinated contrast material (ICM) continue to be a significant medical problem. Complement components were assayed in patients having reactions to evaluate the possibility of complement activation in these reactions. Reactor group samples were drawn from patients during the contrast reactions and then 2 weeks later to provide the equivalent of preinjection baseline samples, Control patient values were determined from blood samples drawn from patients before and 20 minutes after ICM injections without reaction. There were consistent falls in total hemolytic complement (CH50) as well as C3, C4, and C5 in both the control group and the reactor group. These falls in the complement reached statistical significance only for CH50 in the reactor group. The results indicate that complement activation occurs after ICM injection. This activation can occur independent of clinical reactions; however, falls in total hemolytic complement and low hemolytic complement titers prior to ICM infusion may be related to the presence of anaphylactoid symptoms.