Parathyroid Hormone Intraoperative

Primary hyperparathyroidism affects approximately 1 in 700 people. Surgery is currently the only curative therapy for parathyroid adenoma and hyperplasia. Typically there are 4 glands, but 2 - 6% of individuals have more than 4 glands and some individuals may have as many as 12 glands. Approximately 15% of patients have parathyroid glands in ectopic locations such as the thymus, perithymic tissue, and thyroid nodules. The most common cause of unsuccessful parathyroid surgery is failure to recognize multiglandular disease, which has a reported incidence of 8 to 35%. Multiglandular disease occurs most frequently in patients with multiple endocrine neoplasia (MEN) type 1, familial hyperparathyroidism, and secondary hyperparathyroidism. Missed multiglandular disease necessitates re-exploration, which has a substantially increased risk of complications such as permanent hypoparathyroidism and recurrent laryngeal nerve paralysis.  

Rapid intraoperative PTH assays have been introduced to assist in determining when all hyper-functioning parathyroid tissue has been resected. The half-life of PTH varies between 2 and 5 minutes.  Therefore, removal of an abnormal gland can be assessed by a decrease in plasma PTH within 10 minutes after resection.  A typical intraoperative PTH protocol involves the following steps. 

• Induce anesthesia
• Draw a baseline PTH level
• Isolate enlarged parathyroid gland
• Resect parathyroid gland
• Wait ten minutes
• Draw post-resection PTH level

A decrease in the post-resection PTH level of >50% compared to the baseline or second sample indicates that all abnormal parathyroid tissue has been removed. A lesser decline indicates that further exploration is warranted.  An example of a successful resection is illustrated below. 

Surgery needs to notify the laboratory the day before the procedure to schedule testing. Specimen requirement is one lavender top tube of blood. The tube needs to be completely filled with blood, because excess EDTA anticoagulant may interfere with PTH measurement. Specimens should be placed in a cup of ice and immediately transported to the laboratory. Results are called to the operating room and reported in the laboratory information system. 

References

Wilhelm SM, et al, The American Association of Endocrine Surgeons guidelines for definitive management of primary hyperthyroidism, JAMA Surg, 2016;15(10):959-968.

Medas F, et al, The role of Rapid Intraoperative Parathyroid Hormone (ioPTH) assay in determining outcome of parathyroidectomy in primary hyperparathyroidism: A systematic review and meta-analysis, Internat J Surg, 2021;92:106042.