Postoperative calcium levels as a diagnostic measure for hypoparathyroidism after total thyroidectomy

The aim of the present study was to identify a fast, efficient and low-cost method to diagnose hypoparathyroidism after total thyroidectomy.

One hundred and forty medical records, which contained patients' clinical and laboratory data, were retrospectively analyzed. Patient parathyroid hormone values, which were obtained immediately following operation, were compared with their ionized calcium levels the morning after surgery. This comparison was used to examine the correlation between the two variables in predicting hypoparathyroidism because measuring calcium levels is low-cost and more available in the hospitals compared to measuring parathormone (PTH) levels.

There was a positive and statistically significant correlation between PTH and ionized calcium values (Pearson correlation coefficient, r = 0.456; p < 0.0001). The values of first postoperative day ionized calcium levels (stratified by the 1.10 mmol/l cut-off value) were tested as a diagnostic measure for hypoparathyroidism, and a PTH < 15 pg/mL obtained immediately following operation served as a reference. This analysis showed that ionized calcium levels measured on the first postoperative day had a sensitivity of 45.6% (95% CI 30.9-61.0%), a specificity of 88.9% (95% CI 80.5-94.5%) and an accuracy of 76.7% (95% CI 68.7-83.5%) as a diagnostic measure for hypoparathyroidism.

In conclusion, we demonstrated that patients who had high ionized calcium levels on the first postoperative day also had high PTH levels immediately following operation and, therefore, they had lower rates of hypoparathyroidism.