Histamine release and complement changes following injection of contrast media in humans.

Mechanisms responsible for allergic-like reactions following administration of radiographic contrast media (RCM) are unclear. Aortic root blood specimens were obtained sequentially in 6 subjects following injection of RCM into the pulmonary artery during cardiac catheterization. In 5 subjects, elevated plasma histamine levels (up to 80 ng/ml) occurred within minutes. Levels of C3, C4, factor B, and total hemolytic complement activity were decreased in the same specimens. No hemodynamic or clinical abnormalities were noted. These findings support the concept that RCM can liberate histamine in vivo in humans. Complement alterations may be related to localized RCM-protein interaction. It is unclear whether complement changes are related to the RCM-induced allergic mediator release.