An individual approach to intraoperative parathyroid hormone measurement during total thyroidectomy.

Purpose: Hypocalcemia is a common complication of thyroidectomy. Measurement of the intraoperative serum parathyroid hormone (PTH) levels became an established technique but it requires further improvements. We aimed to assess intraoperative PTH level testing results against the hypothesis that the PTH assay may be performed almost immediately after thyroid gland removal.

Methods: A retrospective cohort study. During total thyroidectomy surgery, the patients had PTH levels measured at the cutting time and again immediately after the thyroid gland is removed. Post-operatively, serial total blood calcium levels were obtained twice daily and recorded.

Results: Among 63 enrolled patients, 39 had multinodular goiter, 15 thyroid carcinoma, and nine had Graves' disease. The mean age was 59.8 ± 15.3 years, 43 females. The mean PTH level before surgery was 45.8 ± 22.0 pg/mL. Post-operatively, 11/63 patients developed hypocalcemia with serum calcium levels <8 mg/dL. Four patients with ≥50 % decrease in PTH concentration were normocalcemic a day after surgery and were discharged early. Four patients with ≥70 % PTH decrease were treated accordingly during prolonged hospitalization and did not suffer from permanent hypocalcemia. The cut-off value of 70 % decrease after the gland removal was able to predict postoperative hypocalcemia with a sensitivity of 100 %, specificity 82.9 %, PPV 60.0 % and NPV 100 %.

Conclusion: Measurements of intraoperative PTH may not be performed at fixed time intervals but after 1-2 min after removal of the thyroid gland. Defining those not at risk would allow the majority of patients to be waived from post-operative blood calcium testing and safely discharged early after surgery.