Assays for Plasma Complement Activation by X-ray Contrast Media

Hemolytic complement activity and a C3a radioimmunoassay (RIA) were investigated for their ability to characterize contrast media (CM) with respect to complement activation. The CM tested were commercial formulations of diatrizoate, iodamide, iothalamate, ioxaglate, iohexol, and iopamidol. When plasma was exposed to CM, the hemolytic complement activity decreased and the C3a concentration increased. The C3a assay had a larger dynamic range and therefore more ability to discriminate among the CM. Using C3a data from pooled plasma or from individual donors' plasma, nonionic iopamidol (as Isovue 300) had lower complement-activating potential (P less than .005 and P greater than .05, respectively) than all of the ionic media based on diatrizoate, iothalamate, iodamide, and ioxaglate. The ranges of mean C3a values generated by saline, nonionic CM, and ionic CM were 48 to 60, 65 to 173, and 807 to 3272 ng C3a/50 microL, respectively. Complement activation was found to correlate with osmolality (r = 0.945, all media) and with molarity (r = 0.994, diatrizoates).