Intraoperative parathyroid hormone as an indicator for parathyroid gland preservation in thyroid surgery.

BACKGROUND: Intra-operative parathyroid hormone (PTH) levels have successfully been used to assess surgical ablation of parathyroid adenomas, the use of this same test to predict preservation of viable gland has not been widely used. AIM: to test the sensitivity and specificity of intraoperative rapid PTH assay test in predicting permanent postoperative hypoparathyroidism, and applicability to guide the search for inadvertently removed parathyroid glands for possible auto transplantation. PATIENTS AND METHODS: 52 patients undergoing total thyroidectomy for non-malignant thyroid diseases were included. Intraoperative rapid PTH assay test was performed. If levels were reduced, or less than 3 parathyroid glands were detected, removed thyroid gland was examined for unintentionally removed parathyroid tissue for possible auto transplantation.
RESULTS: There was a strong correlation between intraoperative rapid PTH assays and those taken 24 hours after surgery, 16 out of 52 patients had reduction of the PTH intraoperatively to levels below 25 pg/ml, of them, 11 patients (who had values between 15-24 pg/ml) recovered to normal PTH levels within 4 weeks, while the 5 patients with intraoperative PTH levels below 15 pg/ml failed to regain normal PTH levels up to 12 weeks postoperatively, even in those patients where parathyroid tissue was auto transplantated. The 4 patients who had parathyroid tissue reimplanted intraoperatively restored some of their parathyroid function as indicated by relative rise of their PTH levels, but did not reach even the low normal levels. (ROC) curve for prediction of early hypoparathyroidism using intraoperative rapid PTH assay was statistically highly significant with optimal cutoff value for predicting early hypocalcaemia level <27 pg/ml, (sensitivity 100%, specificity 68.2%). (ROC) curves for predicting permanent hypoparathyroidism using intraoperative rapid PTH assay or standard PTH assay taken 24 hours after surgery were statistically significant with optimal cutoff value PTH level <12 pg/ml on the intraoperative PTH curve or <15 pg/ml on the postoperative PTH curve (sensitivity 100%, specificity 100%).
CONCLUSION: Intraoperative PTH assay may allow intraoperative monitoring of parathyroid function, predicting postoperative outcomes, may identify patients at risk of developing postoperative hypoparathyroidism, guiding surgeons to re-examine removed specimens for inadvertently removed parathyroid tissue with possible auto transplantation, or more practically a guide to early replacement therapy to prevent hypocalcaemia, leading to safe and early hospital discharge. Limitations in our study to be reconsidered in further studies, are relative small sample size, inability for randomisation, and the variable values reported for the cut off value of PTH causing hypocalcaemic symptoms needing intervention.