The aim of study was to determine the cut-off value of serum parathyroid hormone levels with a predictive value for the occurrence of clinical hypocalcemia following total thyroidectomy.

We performed a retrospective review, of 150 patients who underwent total thyroidectomy for papillary thyroid carcinoma from January 2010 to July 2010. We measured the serum levels of parathyroid hormone and phosphate within 18~24 hours postoperatively. The serum levels of ionized calcium were measured immediately and within 18~24 hours postoperatively. We also determined the cut-off value, sensitivity and specificity of serum levels of parathyroid hormone, ionized calcium, and phosphate with a predictive value for the occurrence of clinical hypocalcemia.

Serum levels of parathyroid hormone were 2.0±1.7 pg/ml in the clinical hypocalcemia group, 9.9±10.7 pg/ml in the asymptomatic hypocalcemia group, and 15.3±10.7 pg/ml in the normal control group (P<0.001). Serum levels of ionized calcium were also significantly lower in the clinical hypocalcemia group (0.92±0.16 mmol/L) compared with the normal control group (P=0.002). On the other hand, serum levels of phosphate were significantly higher in the clinical hypocalcemia group (P=0.009). The cut-off value of serum parathyroid hormone levels for the prediction of clinical hypocalcemia was 4.5 pg/ml, where the sensitivity, specificity, positive predictive value, and negative predictive value were 87.5%, 63.4%, 89.3% and 59%, respectively.

Serum parathyroid hormone levels following total thyroidectomy are the most powerful predictive factors for the occurrence of clinical hypocalcemia. Our results show that the incidence of clinical hypocalcemia is relatively higher at postoperative serum levels of parathyroid hormone ≤4.5 pg/ml.