The Importance of Level of Drop of Intra-operative Parathyroid Hormone in Predicting Recurrence After Parathyroidectomy for Primary Hyperparathyroidism

Background: During parathyroidectomy for hyperparathyroidism, intraoperative parathyroid hormone (IOPTH) levels are used to confirm excision of parathyroid adenoma. A drop in IOPTH level of 50% or drop to a normal level is associated with a high cure rate. However, there are still a number of patients who fit this criterion who have recurrent hyperparathyroidism. The authors hypothesize that a drop in PTH to a level below 4 pmol/l (37.72 pg/mL) rather than just a 50% drop would decrease the rate of recurrence disease. Methods: The authors conducted a retrospective review of consecutive patients who underwent surgery for parathyroid adenoma between March 2015 and December 2018. Parathyroidectomy was performed with curative parathyroidectomy defined as drop in IOPTH below 4 pmol/l (37.72 pg/mL) after 10-15minutes from excision (2-3 half-life periods of PTH) of abnormal Parathyroid gland. Results: 72 patients were identified who underwent Parathyroidectomy for primary hyperparathyroidism during the study period. Post resection IOPTH levels below 4 pmol/l correctly predicted an operative success rate near 100% in the cohort. Contrarily IOPTH level drop more than 50% but above a level of 4 pmol/l (9 cases) was associated with an additional unidentified Parathyroid adenoma in 7 cases. Conclusions: Post parathyroidectomy drop in IOPTH level below 4 pmol/l appears to be more predictive of successful treatment for primary hyperparathyroidism related to parathyroid adenoma compared to standard criteria.