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

ObjectiveThe aim of the present study was to identify a fast, efficient and low-cost method to diagnose hypoparathyroidism after total thyroidectomy.Materials and methodsOne 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.ResultsThere 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.ConclusionIn 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.

**研究目的** 本研究旨在探寻一种快速、高效且低成本的全甲状腺切除术（total thyroidectomy）后甲状旁腺功能减退症（hypoparathyroidism）诊断方法。
**材料与方法** 本研究回顾性分析了140份包含患者临床及实验室检测数据的病历资料。将患者术后即刻检测的甲状旁腺激素（parathyroid hormone, PTH）水平，与术后次日晨的离子钙（ionized calcium）水平进行对比。鉴于离子钙检测成本低廉且院内可及性优于甲状旁腺激素检测，本对比旨在探讨两项指标在预测甲状旁腺功能减退症中的相关性。
**结果** 甲状旁腺激素与离子钙水平呈正相关且具有统计学显著性（皮尔逊相关系数r=0.456，p<0.0001）。以术后即刻甲状旁腺激素<15 pg/mL作为诊断参照标准，以术后次日晨离子钙水平（以1.10 mmol/L为截断值分层）作为甲状旁腺功能减退症的诊断指标进行检验。结果显示，术后次日晨离子钙水平用于诊断甲状旁腺功能减退症的灵敏度为45.6%（95%置信区间CI：30.9%~61.0%），特异度为88.9%（95%CI：80.5%~94.5%），准确度为76.7%（95%CI：68.7%~83.5%）。
**结论** 本研究证实，术后次日晨离子钙水平较高的患者，其术后即刻甲状旁腺激素水平也更高，因此发生甲状旁腺功能减退症的风险更低。