Accuracy of postthyroidectomy parathyroid hormone and corrected calcium levels as early predictors of clinical hypocalcemia.

OBJECTIVE

To evaluate the accuracy of measurement of different parathyroid hormone (PTH) and corrected calcium (cCa) levels at different times as early predictors of postthyroidectomy hypocalcemia.

DESIGN

A retrospective cohort study.

SETTING

King Fahad Medical City, Riyadh, Saudi Arabia, between January 2006 and March 2009.

METHODS

Patients who underwent total or completion thyroidectomy were followed until hospital discharge. Patients were observed clinically for hypocalcemia; at the same time, the postoperative PTH and cCa levels after 6, 12, and 20 hours and then twice daily were recorded.

MAIN OUTCOME MEASURES

Postthyroidectomy hypocalcemia.

RESULTS

Seventy-nine of 116 patients were enrolled in our study; 26.60% of them had hypocalcemia. PTH measurement at 6 hours postoperatively was an excellent predictor of hypocalcemia (area under the curve = 0.95, 95% CI 0.88-0.99). The mean PTH at 6 hours for hypocalcemic patients was 0.93 (+/- 0.60). A 1.7 pmol/L as a cutoff level of PTH at 6 hours has 95.2% sensitivity, 89.7% specificity, 76.9% positive predictive value (PPV), and 98.1% negative predictive value (NPV). On the other hand, a 2.1 mmol/L as a cutoff level of cCa has 81.0% sensitivity, 81.6% specificity, 65.3% PPV, and 90.9% NPV in predicting hypocalcemic patients.

CONCLUSIONS

PTH measurement 6 hours after surgery with a cutoff level of 1.7 pmol/L is more accurate than serial calcium level measurement for early prediction of patients at risk of hypocalcemia. Thus, a single PTH measurement postoperatively will help in discharging patients safely within the first 24 hours, improving bed use and cost-effective care.