Evaluation of the diagnostic utility of the aminotransferase/lactate dehydrogenase ratio for the suspension of tissue specimens during thyroid surgery for the identification of parathyroid tissue

Identification of the parathyroid glands during surgery is crucial for preventing postoperative hypoparathyroidism. Kikumori et al. reported that the aspartate aminotransferase (AST)/lactate dehydrogenase (LDH) ratio for the saline suspension of a suspicious tissue can differentiate parathyroid tissue from other tissues. The aim of this study was to evaluate the utility of this method and investigate the appropriate time for measurement. We obtained 465 tissue specimens during thyroidectomy of 102 patients with papillary thyroid carcinoma (PTC), and 422 specimens (129 parathyroid, 92 PTC, and 201 other tissues) with measurable AST and LDH were analyzed. Small pieces of the tissues were immersed in saline and sent for measurement of AST and LDH. The assay was performed immediately after thyroidectomy for 245 specimens (the same-day group) and during the next morning for the remaining 177 specimens (the next-day group). The accuracy of diagnosing parathyroid tissue was significantly better in the same-day group than in the next-day group. A cut-off value of 0.18 gave the best diagnostic precision, with an area under the receiver operating characteristic curve of 0.95 and 88.7% sensitivity and specificity in the same-day group. When the cut-off value was set to 0.20, the specificity for excluding carcinomatous tissues was 100%. When measured on the day of the surgery, the AST/LDH ratio for the saline suspension of the surgical specimens is useful for discriminating parathyroid tissues from other tissues. This method can be utilized at most hospitals where intraoperative frozen sections or rapid parathyroid hormone assays are not available.