Estimation of free calcium levels after thyroidectomy

Total calcium is routinely measured after thyroidectomy in a clinical setting, while the measurement or calculation of the free calcium level is not generally performed. We reviewed total and free calcium levels in patients who underwent lobectomy (n = 15), subtotal thyroidectomy (n = 15) and total thyroidectomy (n = 15). Postoperative total calcium levels decreased significantly in comparison to preoperative levels in all thyroidectomies (p < 0.01), and this fall was significantly related to the extent of surgery (p < 0.01). In contrast, there was no significant difference between preoperative and postoperative free calcium levels in patients undergoing lobectomy, although we found a decrease in free calcium levels after both subtotal and total thyroidectomy. Total protein levels decreased regardless of the type of operation. Serum total calcium levels were thought to be altered by serum protein levels through the change of protein-bound calcium levels. When examined for free calcium levels, some patients were administered unnecessary calcium supplementation because hypocalcemia had been judged from the total calcium level. Since the wrong diagnosis may be given with regard to hypoparathyroidism by measurement of total calcium levels alone, we propose that free calcium levels should be routinely measured or calculated after thyroidectomy.