Early prediction of hypocalcemia after thyroidectomy using parathyroid hormone: an analysis of pooled individual patient data from nine observational studies

BACKGROUND: Monitoring for hypocalcemia after thyroidectomy, using only symptoms and serum calcium levels, can delay the discharge of patients who will remain normocalcemic and can delay the treatment of hypocalcemic patients. STUDY DESIGN: We conducted a systematic search for articles describing use of parathyroid hormone (PTH) assay, checked within hours of completing thyroidectomy, to predict postoperative symptomatic hypocalcemia. Studies were excluded if all patients were treated with postoperative calcium, or if early PTH values were used to alter management of the patient. Individual patient data (perioperative PTH and calcium levels, development of hypocalcemia) were obtained for 457 patients from the corresponding authors of 9 studies and pooled to yield the following results. RESULTS: PTH, checked at three time periods after removal of the thyroid gland (0 to 20 minutes, 1 to 2 hours, and 6 hours), was substantially lower in patients who became hypocalcemic compared with those who remained normocalcemic. The accuracy of PTH in determining hypocalcemia increased with time and was excellent when checked 1 to 6 hours postoperatively. A single PTH threshold (65% decrease compared with preoperative level), checked 6 hours after completing thyroidectomy, had a sensitivity of 96.4% and specificity of 91.4% in detecting postoperative hypocalcemia. CONCLUSIONS: PTH assay, when checked 1 to 6 hours after thyroidectomy, has excellent accuracy in determining which patients will become symptomatically hypocalcemic. Routine use of this assay should be considered because it may allow earlier discharge of the normocalcemic patient and earlier identification of patients requiring treatment of postthyroidectomy hypocalcemia.