Is Preoperative Vitamin D Deficiency a Predictor of Transient and Permanent Hypocalcemia After Total Thyroidectomy? A Cohort Study in a Tertiary Care Hospital

The role of vitamin D as a predictor of postoperative hypocalcemia after total thyroidectomy (TT) has variable reports as it is latitude and population specific. This cohort study in South India evaluated the impact of preoperative serum 25-hydroxycholecalciferol (25OHD) levels on transient and permanent hypocalcemia (> 6 months) post-TT. Consecutive patients (n = 327; median age = 34 years; man:woman = 65:262) undergoing TT for benign or malignant thyroid diseases were evaluated for serum corrected calcium, intact parathormone and 25OHD (categorized as severe deficiency < 10; deficiency = 10–19.9; insufficiency = 20–29.9; sufficiency = 30–100 ng/mL) at baseline, 48-h and 6-month post-TT. The incidence of transient and permanent hypocalcemia (calcium < 8 mg/dL) post-TT was 33.3% and 7.9%, respectively, and preoperatively 13%. Patients with 25OHD severe deficiency (n = 44), deficiency (n = 131) and insufficiency (n = 109) had 20.2, 4.4 and 4.1 times higher odds of developing transient hypocalcemia, while preoperative hypocalcemia, malignancy, hyperthyroidism, thyroiditis and transient hypoparathyroidism were other significant predictors. Major determinants of permanent hypocalcemia were severe 25OHD deficiency and permanent hypoparathyroidism (each P < 0.05). In receiver operating characteristic, 25OHD reliably predicted transient hypocalcemia with threshold of 18.4 ng/mL. Areas under curve, sensitivity and specificity were 0.661 (P = 0.001), 60% and 59.4%, respectively. Low preoperative calcium and 25-hydroxycholecalciferol levels, widely prevalent in our population, were independent risk factors for transient and permanent hypocalcemia after total thyroidectomy. The risk of post-thyroidectomy hypocalcemia escalated many-fold with decreasing 25-hydroxycholecalciferol levels including insufficient range and prophylactic therapy may facilitate day-care surgery. Trial registration: This study is retrospectively registered with Research Registry and the unique identifying number is Research Registry 5818.