Intraoperative Identification of Parathyroid Tissue Using the Ratio of Aspartate Transaminase to Lactate Dehydrogenase.

Abstract

Introduction: Inadvertent devascularisation or removal of parathyroid glands (PT) during thyroidectomy necessitates their autotransplantation after Frozen section (FS). FS is time-consuming, tedious and expensive, disrupts the pathology department and is not universally available. This study aimed to determine the ratio of aspartate aminotransferase to lactate dehydrogenase (AST/LDH) of PT extracts to differentiate it from fat, thyroid, and lymph node (LN).

Methods: This prospective study was conducted on all patients planned for any thyroid or parathyroid surgery. Intra-operatively, a 2.5 × 2.5 × 2.5 mm³ of the devascularised or inadvertently removed PT was excised, minced in 2 mL normal saline and the supernatant fluid was sent to the standard lab for AST/LDH estimation. The minced tissue was sent for histopathological examination for confirmation. Thyroid, LN and fat samples were taken as controls and analysed similarly. Parathyroid adenoma (PTA) was analysed separately.

Results: The mean AST/LDH ratios of PT (0.311 ± 0.176) were significantly higher than that of thyroid, fat and LN. A cut-off of ≥0.165 for PT had a sensitivity and specificity of 83.8% and 83.1% against thyroid tissue, 83.8% and 74% against fat, and 83.8% and 100% against LN. AST/LDH ratio of PTA was found to be 0.318.

Conclusion: AST/LDH ratio can be a simple, reliable, less labour-intensive method of identification of PT and can be a replacement for FS. The high specificity to differentiate an LN is clinically relevant in central compartment lymph node dissections with a higher probability of inadvertent removal or devascularisation of PT.