The role of parathyroid hormone and serum calcium levels in evaluation of post-thyroidectomy hypocalcemia

Objective: To determine the role of parathyroid hormone and serum calcium level measurements for prediction of hypocalcemia after thyroidectomy Methods: One hundred twenty one consecutive patients undergoing total or completion thyroidectomy between October 2015 and July 2017 were included in the study. Parathyroid hormone, serum calcium and ionised calcium levels were measured preoperatively, 4 hours and 24 hours postoperatively. Demographic data (age, gender), surgical features (type of surgery, neck disection, number of identified parathyroid glands, parathyroid autotransplantation), pathologic evaluation (specimen weight, presence of parathyroid gland in specimen, malign/benign) and other blood tests related with calcium metabolism (serum magnesium, phosphorus, 25-OH vitamin D levels) were also evaluated. Patients having at least one postoperative serum calcium level below 8.0 mg/dL were determined as hypocalcemic. Oral calcium supplementation were given to all patients. Calcitriol and intravenous calcium supplementation was also added as needed for patients with hypocalcemia. Results: Seventeen (%14) of 121 patients who developed postoperative hypocalcemia were named as hypocalcemic group and 104 (86%) patients who did not develop hypocalcemia were named as normocalcemic group. There was no statistically significant difference between hypocalcemic and normocalcemic patients in terms of demographic data (age, gender), surgical features (type of surgery, neck disection, number of identified parathyroid glands, parathyroid autotransplantation), pathologic evaluation (specimen weight, presence of parathyroid gland in specimen, malign/benign) and other blood tests related with calcium metabolism (serum magnesium, phosphorus, 25-OH vitamin D levels) (p>0,05). Postoperative parathyroid hormone and calcium levels were lower in hypocalcemic patients (p<0,05). Sensitivity and specifity of parathyroid hormone concentrations at 4 hour and 24 hour after the surgery were calculated for predicting hypocalcemia. Parathyroid concentration of 14,03 pg/mL measured at 4 hour after surgery had a 94,1% sensitivity and 65,3% spesificity; and parathyroid concentration of 5,89 pg/mL measured at 24 hour after surgery had a 94,1% sensitivity and 70% spesificity for predicting postoperative hypocalcemia. Parathyroid hormone decrement of 81,8% four hours after surgery had 88,2% sensitivity and 82,7% spesificity; and decrement of 85,8% twenty four hours after surgery had 94,1% sensitivity , 73% spesificity for predicting hypocalcemia. Conclusion: Measurement of parathyroid hormone levels at 4 and 24 hours after thyroidectomy reliably predicts hypocalcemia in the early postoperative period and helps identify patients at risk for planning appropriate calcium supplementation. Keywords: thyroidectomy, hypocalcaemia, hypoparathyrodism, parathyroid hormone, complication