Acute hypocalcemic effects of clinical contrast media injections.

A decrease in free ionic calcium levels has been reported in the coronary sinus after coronary artery injections of small doses (9 ml) of radiographic contrast media, but there were no studies of the systemic effects of larger doses of medium. Therefore, the acute effects of two commonly used radiographic contrast media on calcium metabolism were studied in nine patients undergoing angiography and five patients undergoing computed tomography. Free ionic calcium (Ca++) in serum was measured by ion-specific electrode, and immunoreactive parathyroid hormone by a highly sensitive radioimmunoassay. Infusion of Renografin or Reno-M-DIP acutely lowered serum Ca++ and produced an immediate increase in parathyroid hormone in each patient studied. Serum Ca++ fell to or below the lower limit of normal in about half the patients. The changes in Ca++ and parathyroid hormone were 2.5- to 4.5-fold greater than those observed after rapid infusion of equal or larger volumes of normal saline. In vitro, the contrast media had no direct effect on the parathyroid hormone assay, but reduced the Ca++ concentration of aqueous calcium solutions by about the amount predicted from their content of disodium edetate and sodium citrate. Contrast agents that contain divalent cation chelators should be used with care in patients in whom a fall in free ionic calcium might have detrimental effects.