The predictive value of perioperative calcium levels after thyroid/parathyroid surgery

Background. This work was done to determine whether the slope of change between preoperative and early postoperative (2 hr and 8 hr) ionized calcium levels (ciCa) could predict significant postoperative hypocalcemia. Methods. We did a retrospective chart review of 79 patients undergoing thyroid (n = 56) or parathyroid surgery (n = 23) where overall parathyroid function was felt to be at risk. Results/Conclusions. A positive slope between the preoperative ciCa and any postoperative ciCa or the first two postoperative ciCa's predicted normocalcemia in 100% of patients. For the thyroid group, the difference in the slope of the change from preoperative ciCa to first (<2 hours) postoperative ciCa (-15.940%/hours vs -9.375%/hours, p =. 082) did not differentiate patients who developed hypocalcemia (n = 11) and those who remained normocalcemic (n = 45). By contrast the slope of change from preoperative ciCa to the second postoperative (8 hr) ciCa (-1.671%/ hour vs -0.849%/hours, p =. 006) and first to second postoperative ciCa (-1.022%/hour vs -0.473%/hour, p =. 001) did. For the parathyroid group, none of the differences in similar comparisons between the normocalcemic (n = 20) and hypocalcemic patients (n = 3) approached statistical significance. The relatively small number of patients who became hypocalcemic in this study precluded definition of an absolute slope of calcium level change above which normocalcemia can be assured