One hour PTH levels may predict early post-thyroidectomy hypocalcemia

1. Asymptomatic patients with parathyroid hormone (PTH) levels greater than 15 pmol/L at one hour after surgery can be safely discharged. 

2. Patients with PTH levels less than 1.5 pmol/L should be administered a prophylactic dose of calcitriol in order to avoid post-operative hypocalcemia.

Evidence Rating Level: 2 (Good) 

Study Rundown: Parathyroid dysfunction and the subsequent development of hypocalcemia are a known risk following thyroidectomy.  Post-operative symptomatic hypocalcemia is often associated with significant morbidity and a prolonged hospital stay making early detection and administration of calcitriol crucial.  In this study, the authors investigated the role of measuring PTH levels at 1, 6 and 24 hours in predicting early postoperative hypocalcemia. They found that all PTH assays, particularly at 1 hour post-op, provided useful information in distinguishing those that can be safely discharged versus those that require prompt calcium replacement therapy. An important strength of this study is the high sensitivity, specificity, positive and negative predictive values of low one-hour PTH levels. However, a limitation is that it is a retrospective review at a single institution. Although this study is not the first to delineate the role of PTH assays in predicting post-thyroidectomy hypocalcemia, it provides a useful guideline for the optimal time to measure PTH levels in the post-operative period.

Click to read the study in the Canadian Journal of Surgery

Relevant Reading: Low parathyroid hormone levels after thyroid surgery: A feasible predictor of hypocalcemia

In-Depth [retrospective cohort]: This is a retrospective study involving 149 consecutive patients from a single institution. All included patients underwent either total or completion thyroidectomy for malignancy. The normal PTH and calcium levels were defined as 1.5-6.9 pmol/L and 1.1-1.32 mmol/L, respectively. In this study, the authors found that the post-operative incidence of low PTH levels at 1, 6 and 24-hours reached an early plateau and did not vary significantly (1-hour: 34, 22.8%; 6-hours: 36, 24.2%; 24-hours: 38, 25.5%). The mean PTH levels in hypocalcemic patients also plateaued early. In addition, 34 out of 38 hypocalcemic patients had PTH-1 levels less than 1.15 pmol/L, corresponding to the sensitivity and specificity of 89% and 100%, respectively. The negative predictive value and positive predictive value were 97% and 100%, respectively.

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