Systemic hypocalcemia after clinical injections of radiographic contrast media: amelioration by omission of calcium chelating agents.

Intravascular injection of some radiographic contrast media causes a fall in the concentration of unbound serum calcium (Ca++) and an increase in serum immunoreactive parathyroid hormone (iPTH). The decrease in Ca++ levels was attributed to the presence in the contrast media of calcium chelating agents (disodium edetate and sodium citrate) and to the effects of high ionic strength and hemodilution on calcium ion activity. In the present study, we have tested whether omission of the calcium chelating agents from solutions of diatrizoate will lessen the alterations in systemic calcium metabolism. We compared Renografin-76 (RG-76) (diatrizoate meglumine and diatrizoate sodium), which contains disodium edetate and sodium citrate, with Hypaque-76 (H-76) (diatrizoate meglumine, diatrizoate sodium), which contains no calcium chelating activity. A bolus injection of a mean dose of 62 ml of either contrast medium decreased levels of Ca++ significantly (P less than 0.01) at five minutes. The decrease was significantly greater (P less than 0.025) with RG-76 (0.096 +/- 0.018 mM, mean +/- SE) than it was with H-76 (0.049 +/- 0.018 mM, mean +/- SE). The level of iPTH increased (P less than 0.01) by 68 +/- 13 nanoliter equivalents (nleq) per ml with RG-76 and by 28 +/- 8 nleq per ml with H-76 (P less than 0.01 vs RG-76). In vitro, RG-76 decreased levels of Ca++ in aqueous calcium solutions 3.7-fold more than did H-76, but neither contrast medium had any direct effect on the parathyroid hormone assay system. Omission of divalent cation chelating agents from solutions of diatrizoate reduces their effects on systemic calcium metabolism.