One-hour PTH after thyroidectomy predicts symptomatic hypocalcemia

Abstract

Background

A major morbidity after total thyroidectomy is hypocalcemia. Although many clinical factors and laboratory studies have been correlated with both biochemical and symptomatic hypocalcemia, the ideal use and timing of these tests remain unclear. We hypothesize 1-h (PACU) parathyroid hormone (PTH) will identify patients at risk for symptomatic hypocalcemia.

Methods

This prospective study evaluated 196 patients undergoing total thyroidectomy. Serum calcium and PTH levels were measured 1 h after surgery and on postoperative day 1 (POD1). Performance of a central compartment lymph node dissection, parathyroid autotransplantation, indication for procedure, pathology, and presence of parathyroid tissue in the pathology specimen were recorded.

Results

Of 196 patients, nine (4.6%) developed symptomatic hypocalcemia. Thirty four (17.3%) had a 1-h PACU PTH ≤10 pg/dL, whereas 31 (15.8%) had a POD1 PTH of ≤10. Five (56%) of the nine symptomatic patients underwent central compartment lymph node dissection, four (44%) had parathyroid autotransplantation, and four (44%) had a PACU PTH ≤10. PACU and POD1 PTH levels were correlated (R² = 0.682). Multivariate regression identified central compartment dissection, autotransplantation, and PACU or POD1 PTH correlated with symptomatic hypocalcemia. PACU PTH, POD1 PTH, PACU Ca, malignant final pathology, and age ≤45 y correlated with biochemical hypocalcemia.

Conclusions

A 1-h postoperative PACU PTH is equivalent to POD1 PTH in predicting the development of symptomatic hypocalcemia. Biochemical hypocalcemia was not predictive of symptoms in the immediate postoperative period. Lymph node dissection and parathyroid autotransplantation correlated with symptomatic hypocalcemia and improve the sensitivity of biochemical screening alone.

Introduction

One of the most common complications after total thyroidectomy is hypocalcemia. This can be a result of manipulation of the parathyroids during surgery, devascularization of the parathyroids, or from inadvertent removal of the parathyroid gland with the thyroid specimen. Although improvements in surgical technique have made thyroidectomy a safe operation, temporary hypocalcemia still occurs. For routine cases, roughly 5%–10% of patients will develop symptoms of temporary hypocalcemia [1], [2]. Although in more complex cases, such as those requiring lymph node dissection or with a diagnosis of Graves disease, up to 30% of patients will experience symptoms of temporary hypocalcemia [3], [4], [5], [6], [7]. The incidence of permanent hypocalcemia is considerably less (0%–2%) [8], [9], [10], [11].

In recent years, there has been increasing pressure for early discharge of patients undergoing total thyroidectomy. Although some surgeons place all patients on calcium postoperatively, others use this medication more selectively with biochemical and/or clinical factors guiding their decision making. Postoperative parathyroid hormone (PTH) and calcium levels, as well as clinical factors, such as lymph node dissection, autotransplantation, and indication for thyroidectomy have been studied to anticipate the need for calcium supplementation and predict the development of hypocalcemic symptoms. Although biochemical studies of post thyroidectomy patients have demonstrated PTH levels at various times correlate with the development of symptomatic hypocalcemia, the optimal timing remains unclear. Postoperative serum calcium on day 1 has not been shown to consistently correlate with symptomatic hypocalcemia [1], [2], [12], [13], [14], [15], [16], [17], [18].

We sought to compare serum calcium and PTH drawn at two time points, 1 h postoperatively (PACU) and on postoperative day 1 (POD1) to identify which test is the best predictor of symptomatic and biochemical hypocalcemia. Additionally, we aimed to determine whether combining known clinical factors associated with hypocalcemia could improve the sensitivity of biochemical tests alone in predicting postoperative hypocalcemia after total thyroidectomy.