Intraoperative PTH Measurement
as a "Biochemical Biopsy"

Mitchell G. Scott, Ph.D.
Associate Professor, Division of Laboratory Medicine, Washington University; and Associate Medical Director, Clinical Chemistry & Decentralized Testing Barnes-Jewish Hospital, St. Louis, Missouri

The major disease of the parathyroid glands is overactivity of one or more of the typically four glands located in the neck. This condition, known as primary hyperparathyroidism, leads to the overproduction of PTH resulting in an abnormal elevation in serum calcium. The conventional treatment for hyperparathyroidism is surgical removal of the affected gland(s) following bilateral neck exploration with intraoperative frozen section histology to identify the diseased gland(s). This has been an effective approach, with low morbidity and high success rates, but it requires a large transverse incision in the neck under general anesthesia and a one- or two-night hospitalization. Now, preoperative localization of the affected gland using radiologic scans combined with intraoperative PTH measurements allows surgeons to locate more precisely and remove the diseased tissue with less invasive surgery often performed under local anesthesia.

Measurement of intact PTH during surgery can be used as a "biochemical biopsy" to help determine whether the overactive parathyroid tissue has been removed. High levels of PTH before surgery are reduced significantly within minutes of removal of the hypersecreting gland because PTH has a short in vivo half-life of less than 5 minutes and because the normal glands are suppressed and do not secrete PTH immediately. This drop in the PTH level indicates that further dissection and exploration of the remaining parathyroid glands is unnecessary.

Experience using DPC's IMMULITE® Turbo Intact PTH assay at Barnes-Jewish Hospital and Washington University in St. Louis, Missouri, over the past six months showed that the surgical procedure can often be carried out in an outpatient setting under local anesthesia, thus shortening hospital stays. EDTA plasma samples were drawn before surgery and after excision of the diseased gland(s). All patients had one preoperative and at least one postexcision intact PTH (iPTH) assay performed. Successful excision was deemed to be a 50 percent or more drop from baseline iPTH values following excision of the diseased gland(s). Using IMMULITE Turbo Intact PTH, the median time for each iPTH determination (from arrival in the laboratory to assay result) was 17 minutes (range: 14 to 35 minutes). The median time from the first preoperative determination to the last determination, indicating successful surgery, was 58 minutes (range: 23 to 179 minutes). The median drop in iPTH values from baseline was 88 percent.

In addition to the cost-savings associated with shortened hospital stay and decreased exposure to general anesthesia, the use of iPTH testing allows the laboratory staff to contribute directly to patient care. A stronger relationship between the laboratory staff and the surgeons has also developed because of the cooperation needed to implement this testing. The surgeons are pleased with the service they receive from the laboratory and find the iPTH testing a useful adjunct to their surgical procedure.