Vitamin D deficiency and the risk of hypocalcemia following total thyroidectomy

To determine whether patients with vitamin D deficiency (VDD) are at increased risk for hypocalcemia following total thyroidectomy.

A retrospective study of 246 consecutive patients undergoing thyroidectomy at a McGill University teaching hospital was conducted. Patients who had subtotal thyroidectomy or concomitant parathyroidectomy or whose laboratory tests were incomplete for analysis were excluded, as were pediatric patients. The remaining 139 patients had preoperative 25-hydroxyvitamin D [25(OH)D], corrected calcium, and parathyroid hormone (PTH) measured. Postoperatively, PTH and serum calcium were measured to assess for hypocalcemia. Low vitamin D (LVD) was defined as 25(OH)D ≤ 70 nmol/L (≤ 28 ng/mL), which includes vitamin D insufficiency, 25(OH)D > 35 nmol/L (> 14 ng/mL) but ≤ 70 nmol/L (≤ 28 ng/mL), and VDD, 25(OH)D ≤ 35 nmol/L (≤ 14 ng/mL). Adequate vitamin D (AVD) corresponded to levels > 35 nmol/L (> 14 ng/mL), whereas optimal vitamin D (OVD) levels corresponded to levels > 70 nmol/L (> 28 ng/mL).

The rate of postthyroidectomy hypocalcemia in OVD patients was 10.4% (8 of 77) compared to 3.2% (2 of 62) in LVD patients (odds ratio  =  0.29, p  =  .10). There was no hypocalcemia in the 9 VDD patients, meaning that all hypocalcemic episodes occurred in patients with AVD (7.7%; 10 of 130). The mean preoperative PTH levels for LVD patients was 4.65 pmol/L (43 ng/L) compared to 4.18 pmol/L (38.9 ng/L) for OVD patients (p  =  .073).

In this series, preoperative LVD did not predict early postthyroidectomy hypocalcemia. On the contrary, it showed a trend toward protective effect. Adaptive changes in the parathyroid glands, such as hypertrophy, hyperplasia, or the ability to secrete more hormone secondary to prolonged VDD, may contribute to this phenomenon. A large prospective study is needed to better understand the relationship between preoperative vitamin D levels and postoperative hypocalcemia.