7708 Navigating Thyroid Cancer With Differences in Thyroglobulin Assessment Techniques

Abstract Disclosure: M.S. Shah: None. S. Humayon: None. N.A. Mungo: None. This case report delves into the diagnostic journey of a patient with papillary thyroid carcinoma, emphasizing the importance of precise thyroglobulin measurement methods. The case highlights the differences between immunoassay and mass spectrometry in monitoring disease progression and treatment response.A 42-year-old female with a family history of thyroid-related issues, was found to have a thyroid nodule on physical exam. She underwent fine-needle aspiration (FNA) revealing papillary thyroid carcinoma, Bethesda category VI. Lymphatic invasion was present necessitating total thyroidectomy and lymph node dissection. Left level 3 and 4 lymph node excision showing 2 of 15 positive for metastatic papillary thyroid carcinoma without extranodal extension. Left superficial jugular lymph node excision showing 1 of 3 lymph node being positive for metastatic thyroid carcinoma without extranodal extension. RAI therapy and post-ablative scan showed focal moderate increased activity adjacent to the left hyoid bone. CT scan of the neck later showed stable appearance of the thyroidectomy bed with no new suspicious soft tissue mass. A small crescentic focus of enhancing soft tissue medial to the left common carotid artery is favored to represent residual thyroid tissue. Multiple small enhancing lymph node in the left neck at level llB and junction of levels ll and lll. Several of these are new or increased in size from prior examination and somewhat acidly enhanced. Although these are within normal limits by size criteria, recurrent diseases cannot be excluded. She underwent another surgical neck dissection with no cancer found. Given the negative findings, a shift from checking thyroglobulin (TG) from immunoassay to mass spectrometry was ideal.Patient was found to have persistent thyroglobulin elevation with Immunoassay, thyroglobulin level (60.5 ng/mL, n<35 ng/ml), without the presence of TG antibodies, whereas liquid chromatography-tandem mass spectrometry (LC-MS/MS) showing (<0.5 ng/mL), highlighting the methodological divergence. To date she has no imaging concerns and repeat testing from different labs similarly demonstrated undetectably Tg by LC-MS/MS and varying levels when tested by Immunoassay. Her levels by Immunoassay have trended down to her most recent level of (38 ng/ml).This case emphasizes the critical role of accurate thyroglobulin assessment in thyroid carcinoma follow-up. Immunoassay and mass spectrometry present divergent results, with LC-MS/MS proving more reliable in monitoring disease progression but more expensive and time consuming. Clinicians should consider the implications of methodological choices on patient management, particularly in cases of persistent elevation despite treatment. The potential discrepancies between these methods should be emphasized considering the impact on treatment decisions. Presentation: 6/1/2024