Objective: To determine the risk of postthyroidectomy hypocalcaemia by measuring parathyroid hormone (PTH) level after thyroidectomy.
Study design: Cross-sectional study.
Place and duration of study: Baqiyatallah Hospital, Tehran, Iran, from March 2008 to July 2010.
Methodology: All included patients were referred for total or near bilateral thyroidectomy. Serum Calcium (Ca) and PTH levels were measured before and 24 hours after surgery. In low Ca cases or development of hypocalcaemia symptoms, daily monitoring of Ca levels were continued. Data were analyzed using SPSS 20 software (SPSS, Chicago, IL, USA). A p-value less than 0.05 were considered statistically significant. To assess the standard value of useful predictive factors, we used receiver operating characteristic (ROC) curves.
Results: Of total 99 patients who underwent bilateral thyroidectomy, 47 patients (47.5%) developed hypocalcaemia, out of them, 12 (25.5%) became symptomatic while 2 patients developed permanent hypoparathyroidism. After surgery, mean rank of PTH level within the normocalcaemic and hypocalcaemic patients was 55.34 and 44.1 respectively, p=0.052. Twenty four hours after surgery, 62% drop in PTH was associated with 83.3% of symptomatic hypocalcaemic. For diagnosis of symptomatic hypocalcaemia, 62% PTH drop had sensitivity and specificity were 83.3% and 90.80%. The area under the ROC curve for the PTH postoperative and PTH drop for diagnostic symptomatic hypocalcaemia were 0.835 and 0.873 respectively.
Conclusion: Measuring PTH levels after 24 hours postthyroidectomy is not reliable factor for predicting hypocalcaemia itself. For predicting the risk of hypocalcaemia after thyroidectomy it is more reliable to measure the serum PTH level before and after operation and compare the reduction level of percentage of PTH drop for predicting the risk of hypocalcaemia.