Postoperative IPTH compared with IPTH gradient as predictors of post-thyroidectomy hypocalcemia

Abstract

Objectives/hypothesis: Predicting patients' risk for hypocalcemia after thyroidectomy may allow for same-day discharge. This study was designed to compare postoperative intact parathyroid hormone (IPTH) alone with percentage change in IPTH (IPTH gradient) in predicting post-thyroidectomy hypocalcemia.

Study design: Retrospective cohort study.

Methods: Patients undergoing total thyroidectomy by the senior author from May 2015 to May 2016 were included. Serum IPTH was measured preoperatively and 1 hour postoperatively, and IPTH gradient was calculated. Postoperative hypocalcemia was mild (≥8.0, <8.4) or severe (<8.0 and/or hypocalcemic symptoms). Postoperative IPTH and IPTH gradient were compared with hypocalcemia using logistic regression. Receiver operating characteristic analysis of IPTH measures as predictors of hypocalcemia was performed, and the area under the curve (AUC) was calculated.

Results: Overall, 119 patients were included. Forty-seven percent of the patients developed postoperative hypocalcemia, including 26 (22%) with mild and 30 (25%) with severe hypocalcemia. Thirteen patients had hypocalcemic symptoms. Median IPTH gradient and postoperative IPTH each differed significantly by category of hypocalcemia (P < .001). Higher IPTH gradient was significantly associated with odds of severe and symptomatic hypocalcemia (adjusted odds ratio [aOR]: 1.21, 95% confidence interval [CI]: 1.06-1.39 and aOR: 1.34, 95% CI: 1.05-1.71 per 10% increase), whereas lower postoperative IPTH was not (aOR: 1.27, 95% CI: 0.95-1.68 and aOR: 1.44, 95% CI: 0.90-2.31 per 10 pg/mL decrease). The AUC for predicting severe hypocalcemia was nonsignificantly higher for IPTH gradient than postoperative IPTH (AUC = 0.77 vs. 0.69, P = .10). The AUC for predicting symptomatic hypocalcemia was significantly higher for IPTH gradient (AUC = 0.75 vs. 0.72, P = .03).

Conclusions: Our results suggest that the IPTH gradient may be more useful than postoperative IPTH alone in predicting risk of post-thyroidectomy hypocalcemia.

Level of evidence: 4. Laryngoscope, 128:769-774, 2018.

Keywords: IPTH; IPTH gradient; hypocalcemia; thyroidectomy.