Prediction of Hypocalcemia in Postoperative Total Thyroidectomy using Single Measurement of Intra-operative Parathyroid Hormone Level
Somjin Chindavijak MD*
Affiliation : * Department of Otolaryngology, National Cancer Institute, Bangkok, Thailand
Objective : Many varieties of methods using intra-operative PTH have been applied to predict hypocalcemia
after total thyroidectomy. The present study prospectively evaluated the reliability of intra-operative PTH
through a single assay to predict hypocalcemia after total thyroidectomy.
Materials and Methods : Intra-operative PTH were performed before and 20 minutes after total thyroidectomy
for 30 new patients. The calcium level was measured at 24 and 72 hours after surgery. Patients who had serum
calcium < 8.5 mg/dl at 24 or 72 hrs. (hypocalcemia) were compared with normocalcemic patients. The level
of intra-operative PTH was determined to predict post operative calcium level.
Results : Post operative hypocalcemia developed in 20 of 30 patients. Those hypocalcemic patients showed
statistically significant lower intraoperative PTH at 20 minute post total thyroidectomy compared with
normocalcemic patients (mean 9.2 vs 24.7, p = 0.006). Sensitivity, specificity, and accuracy for prediction of
post total thyroidectomy hypocalcemia were 85%, 80%, and 83.3% respectively. The positive predictive value
= 89.5% and negative predictive value = 72.7%. Patients with intra-operative PTH at 20 minute post-total
thyroidectomy < 15 pg/ml required close monitoring.
Conclusion : Intra-operative PTH at 20 minutes after total thyroidectomy can predict impending post opera-
tive hypocalcemia. Based on the result, this can guide which patients will be considered safe, and who can be
discharged early. Furthermore, it is used to closely monitor the calcium level and provide early calcium
supplementation.
Keywords : Intra-operative parathyroid hormone assay, Total thyroidectomy, Hypocalcemia
