Complement activation and histamine release following administration of roentgen contrast media

Anaphylactoid reactions following administration of reontgen contrast media (CM) have occasionally been described. In this investigation, blood samples for nonallergic human volunteers were exposed to the CM iodixanol (Visipaque), iohexol (Omnipaque), ioxaglate (Hexabrix) and metrizoate (Isopaque 350). The degree of activation of the complement cascade and the amount of free histamine in the samples were estimated. By using a hemolytic assay, a dose-independent complement consumption was detected when salt-free dilutions of the CM were added to human serum. Very little complement consumption was detectable when the concentrations, indicating that in the CM solutions were adjusted toward normal plasma concentrations, indicating that the lack of salts in the CM formulations was responsible for causing the consumption of complement rather than the CM molecules themselves. By using ELISA assay for determination of the terminal complement complex (TCC), no increase in TCC level was detected following the addition of iodixanol to human serum. The results indicate that iodixanol does not activate the complement cascade when added to human serum, and that it is unlikely that anaphylactoid reactions observed in man after CM administration are caused by CM-induced anaphylatoxins. No histamine release was observed following the addition of ioxaglate, metrizoate, iohexol or iodixanol to blood from nonallergic individuals.