Use of the parathyroid hormone assay at H6 post thyroidectomy: an early predictor of hypocalcemia

Hypocalcemia linked to a diminished circulating intact parathormone (iPTH) is the most common complication after total thyroidectomy. The objective of this study was to evaluate iPTH as a predictor of post-thyroidectomy hypocalcemia.

Hundred-and-eight patients who underwent total thyroidectomy were included. Blood samples (iPTH, calcium and albumin) were performed at different times: preoperatively (H₀), after removal of the gland (H_drop), 6 h (H₆) and one day (D₁) after the surgery. Hypocalcemia was defined by total calcium corrected by serum albumin ≤ 2.10 mmol/l. The area under the ROC curve (AUC) was used to determine the best cut-off value and predictability of iPTH for hypocalcemia in terms of absolute value (ng/L), decrease in the slope (ng/L) and decline (%) between two times.

The study included 101 patients. Among them, 39 had hypocalcemia (38.6%). At H₆, an iPTH absolute value less than 14.35 ng/L (Se = 0.706; Sp = 0.917) and a decline from the preoperative time of more than 59.5% (Se = 0.850; Sp = 0.820) were predictive of hypocalcemia. Other absolute values, decrease in the sloop and decline between preoperative and postoperative values were less relevant.

The iPTH 6 h after total thyroidectomy is predictive of hypocalcemia. It might be used to identify patients not at risk of hypocalcemia and earlier discharge could be considered.