Does preoperative 25-hydroxyvitamin D status significantly affect the calcium kinetics after total thyroidectomy?

Although previous studies have suggested that low preoperative 25-hydroxyvitamin D (25-OHD) is a risk factor for hypocalcemia after total thyroidectomy, the impact of preoperative 25-OHD on calcium (Ca)/parathyroid hormone (PTH) kinetics in the immediate postoperative period remains unclear. The study compared the postoperative Ca/PTH kinetics between different preoperative 25-OHD levels.

A total of 281 patients who underwent a total thyroidectomy were analyzed. Serum Ca was measured preoperatively within 1 h after surgery (Ca-D0) and on the following morning (Ca-D1). Preoperative 25-OHD was also measured after overnight fasting while postoperative PTH was checked at skin closure on day 0 (PTH-D0) and on the following morning on day 1 (PTH-D1). The Ca/PTH kinetics were compared between three groups (group I: preoperative 25-OHD < 10 ng/mL; group II: 25-OHD = 10-20 ng/mL; group III: 25-OHD > 20 ng/mL).

Group I had significantly lower preoperative Ca (p = 0.016) and Ca-D0 (p = 0.036) but higher PTH-D1 (p = 0.015) than groups II and III. PTH-D0, Ca-D1, and the rate of clinically significant hypocalcemia were similar in the three groups. Group I had a significantly smaller Ca drop (-0.02 vs. 0.01 and 0.02 mmol/L, p = 0.011) and a tendency for a significantly smaller PTH drop (0.4 vs. 0.5 and 1.0 pmol/L, p = 0.073) than groups II and III. PTH-D1 (OR = 1.550) and 25-OHD (OR = 0.958) were independent factors for Ca drop from day 0 to day 1.

Although group I began with lower serum Ca, those patients tended to have a greater PTH response to Ca drop and so preoperative 25-OHD did not significantly affect the overall Ca kinetics from preoperative to day 1.