Parathyroid Hormone Assays following Total Thyroidectomy: Is There a Predictive Value?

ABSTRACT

OBJECTIVES: Parathyroid hormone (PTH) is a risk marker for hypoparathyroidism (hypoPTH). This study aimed to determine the predictive values of early PTH assays carried out at the moment of skin closure (PTH SC), to establish a treatment algorithm, identifying two threshold values. We assessed the reproducibility of this approach with two different immunoassay kits (hypoPTH) after total thyroidectomy, but its practical application is not consensual. STUDY DESIGN: We conducted a prospective descriptive study, including all patients who underwent a total thyroidectomy between March 2012 and November 2013. Postoperative PTH SC levels, corrected calcium on postoperative days, and occurrence of hypoPTH symptoms were collected. RESULTS: Of 257 patients, the rate of hypoPTH was 20%. Threshold values to obtain a 100% positive predictive value to identify patients for whom hypoPTH was absolutely certain were PTH SC <7 ng/L for the Roche kit and PTH SC <4 ng/L for the Beckman-Coulter kit. Threshold values to obtain a 100% negative predictive value to identify patients for whom the absence of hypoPTH was absolutely certain were PTH SC ≥19 ng/L for the Roche kit and PTH SC ≥9 ng/L the Beckman-Coulter kit. CONCLUSIONS: A single serum PTH sampled at skin closure is a reliable test to predict hypoPTH after a total thyroidectomy. The use of a threshold based on a 100% negative predictive value enables patients with no risk of hypoPTH to be safely discharged within the first 24 h postoperatively without unnecessary calcium and vitamin treatment. This medication can be given promptly to patients at risk of hypoPTH to limit the occurrence of hypocalcaemia.