Identification of patients at low risk for thyroidectomy-related hypocalcemia by intraoperative quick PTH

Transient hypoparathyroidism is a frequent and challenging complication following total thyroidectomy. The aim of the study was to identify patients at risk of developing thyroidectomy-related hypocalcemia and symptoms by means of the intraoperative quick parathyroid hormone (PTH) assay.

Eighty-one patients undergoing total thyroidectomy were included in the study. Quick PTH levels were measured at induction of anaesthesia and 10 minutes after total thyroidectomy. A sample of 10 patients who underwent unilateral thyroid lobectomy was considered as a control group. The accuracy of intraoperative PTH decline in predicting postoperative hypoparathyroidism was analysed.

After total thyroidectomy, 27 patients (33.3%) developed postoperative hypocalcemia. Symptoms were reported by 21 patients (25.9%). The mean percentage decline of intraoperative quick PTH was 81% in hypocalcemic compared with 39% in normocalcemic patients (P<0.001), and it was 83% in symptomatic compared with 42% in asymptomatic patients (P<0.001). Mean proportion decline of quick PTH after unilateral lobectomy was 20%, significantly lower than the 53% registered after total thyroidectomy (P=0.005). Analysis of variation of intraoperative quick PTH with the receiver operator characteristics (ROC) curve showed a 75.7% decline as the cut-off value predicting postoperative hypocalcemia with the highest accuracy (91.4%) (sensitivity: 81.5% specificity: 96.3% positive likelihood ratio: 22; negative likelihood ratio: 0.2). Regarding the prediction of postoperative symptoms, a 79.5% decline was the most accurate (92.6%) cut-off point (sensitivity: 76.2% specificity: 98.3% positive likelihood ratio: 46; negative likelihood ratio: 0.2).

Quick PTH monitoring during total thyroidectomy is a useful means for identifying low-risk patients for postoperative hypoparathyroidism and candidates for early, safe discharge. Furthermore, it is an objective method complementary to the surgeon's judgement of the intraoperative function of parathyroid glands, which should be implanted in the event of a 75%-80% decline.