Parathyroid hormone: an early predictor of postthyroidectomy hypocalcemia.

Objective: To determine whether there is a correlation between the level of parathyroid hormone (PTH) soon after thyroidectomy and the development of hypocalcemia.

Study Design: Prospective series of 40 consecutive patients undergoing total thyroidectomy or completion thyroidectomy between January 2001 and October 2002.

Method: Ionized calcium was measured before surgery and at 1, 6, 18, 30, and 42 hours after surgery. PTH was measured before surgery and at 1 and 6 hours after surgery using an assay that accurately measures low levels of PTH. Patients were followed up at 1 week and 3 months after surgery with respect to their symptoms and need for calcium supplementation. Clinically significant hypocalcemia was defined as an ionized calcium level of less than or equal to 0.9 mmol/L.

Results: The incidence of postoperative hypocalcemia was 30% (12/40). The mean PTH level 1 hour after surgery was much lower in patients who ultimately became hypocalcemic than in those who remained normocalcemic (3.8+/- 1.9 vs. 33 +/- 21 pg/mL, P =.001). All patients with a PTH level less than or equal to 8 pg/mL 1 hour after surgery developed hypocalcemia, whereas all those with greater than or equal to 9 pg/mL remained normocalcemic.

Conclusions: A single PTH level of less than or equal to 8 pg/mL 1 hour postthyroidectomy is a strong predictor for the development of clinically significant hypocalcemia. Once validated, this test may serve to identify those who require more intensive monitoring, prompt early therapy in those deemed at risk, and enable confident early discharge in the majority of thyroidectomy patients.