The value of postoperative parathyroid hormone levels in predicting the need for long-term vitamin D supplementation after total thyroidectomy.

BACKGROUND

Few studies have examined the need for vitamin D supplementation after total thyroidectomy. This study examines the role of postoperative day (POD) 1 serum calcium and parathyroid hormone (PTH) levels in predicting the need for long-term vitamin D supplementation after total thyroidectomy.

METHODS

A retrospective, single institutional study of patients who underwent total thyroidectomy between January 2007 and December 2008 was performed. Data collected included extent of surgery, final pathology, postoperative calcium (mg/dl) and PTH (pg/ml) values, and duration of vitamin D supplementation. Patients were divided into 4 groups based on POD1 PTH values: group 1 (<5.0); group 2 (5.0-10); group 3 (10.1-20); and group 4 (>20).

RESULTS

Of the 104 patients, 26 were in group 1, 12 in group 2, 18 in group 3, and 48 in group 4, with median PTH values of <2.5, 8.2, 14.1, and 30 pg/ml, respectively. All 7 (7%) patients who required vitamin D supplementation >1 month were in group 1. The positive predictive value of POD1 PTH <5.0 in predicting supplementation >1 month was 27% (sensitivity 100%, specificity 80%). Seventy-eight patients had a POD1 PTH level ≥5, and none required vitamin D supplementation >1 month (100% negative predictive value). The positive predictive value of various POD1 calcium thresholds (<7.5, <8.0, and <8.5 mg/dl) was 17, 14, and 15%, respectively.

CONCLUSIONS

Postoperative PTH levels better predict long-term hypocalcemia requiring vitamin D supplementation than serum calcium levels. A PTH level ≥5.0 may identify patients who can be safely discharged without routine vitamin D supplementation.