Clinical application of the ultrasound‐guided fine needle aspiration for thyroglobulin measurement to diagnose lymph node metastasis from differentiated thyroid carcinoma‐literature review

Papillary thyroid carcinoma (PTC) generally has a good prognosis, but disease recurs in 25% to 30% of PTC patients and significantly reduces the survival rate. Lymph node metastasis (LNM) is reported in 20% to 50% of PTC patients, mainly in the neck, and 20% originates from recurrence. LNM of papillary thyroid carcinoma are a plausible prognostic factor to determine disease recurrence. Currently, fine needle lymph node aspiration for cytology (LN‐FN‐cytology) is the best modality to diagnose LNM but is limited by diagnostic sensitivity and sample error. Fine needle lymph node aspiration for thyroglobulin measurement (LN‐FNA‐Tg) could offer a reliable and quantitative diagnostic method for LNM. The combination of LN‐FNA‐cytology and LN‐FNA‐Tg could achieve almost 100% diagnostic sensitivity and specificity for LNM. Both treatment guidelines of the American Thyroid Association and European Thyroid Association recommend LN‐FNA‐Tg to diagnose LNM after total thyroidectomy. Diagnostic accuracy of the LN‐FNA‐Tg depends on optimal equipment, scanning protocol, skill, and experience of operators. Normal saline is mainly used for aspiration needle wash‐out and buffer solution. And radioimmunoassay or immunoradiometric assay are widely used for the LN‐FNA‐Tg measurement. So far, there is no consensus about the diagnostic threshold of LN‐FNA‐Tg for positive LNM, but high LN‐FNA‐Tg, especially higher than 10 ng/mL, strongly favors LNM.