Validation of a method to replace frozen section during parathyroid exploration by using the rapid parathyroid hormone assay on parathyroid aspirates

Rodney K Chan, Shahrul I Ibrahim, Peter Pil, Francis D Moore, Jr.
Brigham and Women's Hospital, Boston, MA

Objective:
To assess measurement of parathyroid hormone (PTH) content of tissue aspirates as a method to replace frozen section identification of parathyroid tissue during parathyroid surgery.
Design:
Prospective data collection.
Setting:
Tertiary care hospital, single surgeon.
Patients:
172 consecutive patients completing limited parathyroidectomies.
Interventions:
Parathyroid adenomas removed during limited parathyroidectomy were aspirated through a 21-gauge needle. Samples were then assessed for PTH content in parallel to the serial blood sample being run routinely to assess the physiologic impact of the surgery.
Main Outcome Measures:
PTH content of tissue aspirates was compared to histologic identification of removed putative parathyroid tissue.
Results:
Elevated tissue PTH content was associated with the identification of parathyroid tissue in every case. Aspirates from pathologically proven parathyroid tissue had a mean PTH of at least 1691pg/cc, with 160 of the aspirates exceeding the upper limit of the assay. This was significantly higher than values obtained from thyroid aspirates, which had a mean PTH of 88pg/cc(p<0.01), reflective of blood levels at the time of aspiration. Using the 99% confidence interval of known parathyroids as the lower limit of a positive test result, tissue aspirate PTH assay has a positive predictive value of 99% and a negative predictive value of 93%.
Conclusions:
Positive identification of removed tissue as parathyroid is a necessary adjunct to limited parathyroid exploration, where false positive blood PTH drops can result from operative manipulation of the neck. Analysis of tissue PTH content using the same assay as assessing blood PTH concentration is an efficient and accurate method for identifying the tissue with certainty.

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