Robust, quick, and convenient intraoperative method to differentiate parathyroid tissue

Background: Identification of parathyroid tissue during surgery is necessary for its preservation in situ or for autotransplantation to avoid postoperative hypoparathyroidism. Frozen sections are the gold standard for distinguishing parathyroid tissue from other tissues during thyroidectomy. Although frozen sections are very accurate, they are costly and require pathologists and technical staff. Parathyroid tissue is rich in mitochondria, which harbor Krebs-cycle enzymes such as aspartate aminotransferase. In contrast, lactate dehydrogenase is expressed ubiquitously. These 2 enzymes are measured routinely as "leaked" enzymes. We hypothesized that the aspartate aminotransferase-to-lactate dehydrogenase ratio in suspended tissue could distinguish parathyroid tissue from other tissues.

Methods: We analyzed 94 specimens (43 parathyroid, 19 thyroid cancers, 13 normal lymph nodes, 10 adipose, 6 thyroid, and 3 miscellaneous tissues) from 55 patients who underwent thyroid or parathyroid surgery between March 2018 and June 2019 in our institution. Trace amounts of remnant parathyroid tissue from autotransplantation specimens were suspended in 1 mL of normal saline and measured for aspartate aminotransferase and lactate dehydrogenase. Approximately 1 mm³ of apparently distinct tissue minced by scissors (eg, thyroid gland, metastatic lymph node, etc) or washouts of needles used for preoperative aspiration biopsy were also measured for comparison.

Results: The aspartate aminotransferase-to-lactate dehydrogenase ratios in suspended parathyroid tissue specimens were consistently greater than those of other tissues (P < .001, Mann-Whitney test); 0.27 was the optimal cutoff value with 100% sensitivity and specificity.

Conclusion: This method distinguished parathyroid tissue quickly and conveniently from other tissues intraoperatively with minimum cost and without dedicated pathologic staff. This methodology may serve useful in decreasing the incidence of postoperative hypoparathyroidism, especially in settings with limited access to pathologists.