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 (R(2) = 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.

Keywords: Calcium; Hypocalcemia; PTH; Symptomatic hypocalcemia; Thyroidectomy.

Figure 1

Post-operative calcium levels (mg/dL) measured in PACU and on POD1 listed by those with a PACU PTH of ≤10 pg/dL and those with a PACU PTH >10 pg/dL

Figure 2

PACU versus POD1 PTH levels. PACU PTH was found to correlate highly with POD1 PTH (R²=0.682)

Figure 3

Receiver operating characteristic curve of the ability to predict symptomatic hypocalcemia for PTH alone AUC=0.65 (95% CI 0.48-0.82) and PTH with clinical factors AUC=0.75 (0.55-0.95) (p=0.20).

Figure 4

Receiver operating characteristic curve of the ability to predict biochemical hypocalcemia for PTH alone AUC=0.59 (95% CI 0.53-0.66) and PTH with clinical factors AUC=0.67 (0.59-0.75) (p=0.02).