Tan Tock Seng Hospital1
The optimal use of parathyroid hormone (PTH) in the prediction of hypocalcemia after thyroidectomy is unclear. We aim to determine the performance of a practical, 3-categorical classification of postoperative PTH in the prediction of hypocalcemia in patients with and without prophylactic calcium supplementation.
We retrospective studied all patients who underwent total and completion thyroidectomy between 2012 and 2014 in Tan Tock Seng Hospital, Singapore to determine the association of 3 categories of PTH with hypocalcemia in univariate and multivariate analysis.
Forty-one out of 109 patients had prophylactic calcium supplementation after thyroidectomy whereas 68 had not. In both scenarios, PTH of ≥ 1.6 pmol/L, 0.6 to <1.6 pmol/L and < 0.6 pmol/L showed sequentially rising odds ratios for hypocalcemia (p= 0.045 and 0.004, respectively). On multivariate analysis, PTH was the strongest determinant of hypocalcemia regardless of calcium supplementation (p= 0.058 and 0.007, respectively). PTH <1.6 pmol/L performed the best among the 3 categories, with a sensitivity of 75% and 80%, specificity of 62% and 74% in patients with and without prophylactic calcium supplementation, respectively. The specificity of PTH improved further if it remained < 0.6 pmol/L the morning after thyroidectomy in the 49 patients who had repeated PTH measurements (84% vs. 78%, respectively).
Categorizing post-thyroidectomy PTH into ≥1.6, 0.6 to <1.6 and <0.6 pmol/L can triage patients into increasing likelihood of hypocalcemia. PTH that is persistently < 0.6 pmol/L indicates a high likelihood of hypocalcemia. This knowledge may help the clinicians tailor prophylactic calcium supplementation in order to prevent symptomatic hypocalcemia.