Risk factors for hypercalcemia induced by active vitamin D derivatives during supplementation for post-total thyroidectomy hypoparathyroidism.

BACKGROUND

Hypoparathyroidism with hypocalcemia is a frequent complication of total thyroidectomy, occurring in 20%-30% of cases, managed by supplementation, sometimes requiring active vitamin D, which can induce iatrogenic hypercalcemia. Predictive factors for this complication remain poorly defined.

METHODS

We retrospectively analyzed 198 patients who underwent total thyroidectomy at Lille University Hospital between 2018 and 2025 and developed postoperative hypoparathyroidism with hypocalcemia requiring supplementation (calcium, magnesium, and active vitamin D). Patients were divided into those who developed iatrogenic hypercalcemia (28 patients) and those with an uncomplicated course under supplementation (170 patients). Clinical, biological, and therapeutic parameters were compared.

RESULTS

Iatrogenic hypercalcemia occurred in 14% (28/198), always within the first postoperative month; 25% of these required hospitalizations. The 2 groups were comparable for age, sex, body mass index, surgical indications, type of procedure, preoperative serum calcium, 25-hydroxyvitamin D, parathyroid hormone, and thyroid-stimulating hormone. Patients with hypercalcemia had significantly lower early postoperative parathyroid hormone (postoperative day 1 and postoperative day 2, P < .05) and received active vitamin D earlier (1.14 ± 0.65 vs 1.60 ± 0.95 days, P = .002). Neither the preoperative measures, nor the overall trends in serum calcium and phosphate, nor the predictive score for postoperative hypocalcemia predicted iatrogenic hypercalcemia.

CONCLUSION

Iatrogenic hypercalcemia complicates approximately 1 in 7 cases of postoperative hypoparathyroidism. This complication may be severe and may require rehospitalization. Hypercalcemia appears to be associated with low early postoperative parathyroid hormone levels and earlier initiation of active vitamin D. These results emphasize the importance of cautious dose adjustment of supplementation and close monitoring of the calcium-phosphate profile during the first postoperative weeks.