Interpretation of FNA thyroglobulin level in post total or near-total thyroidectomy patients:
Less than
0.9 ug/L
: normal
Between 0.9 - 10 ug/L
: Indeterminate. Those with serum TSH more than 0.4 mU/L and serum thyroglobulin more than 0.2 ug/L are more likely to have metastatic differentiated thyroid cancer in the lymph node. Suggest correlate with clinical history, cytology and imaging findings.
Greater than
10 ug/L
: Provided the aspirate is not from a thyroid remnant or nodule, it is suggestive of metastatic differentiated thyroid cancer (or ectopic thyroid tissue) in the lymph node. A level of more than 100 ug/L is very specific. Suggest correlate with clinical history, cytology and imaging findings.
The diagnostic performance of this test in detecting local lymph node recurrence in post thyroidectomy patients is better than for pre-operative staging in thyroid intact patients. The cut point for thyroid intact cases is generally higher than for post-thyroidectomy but the exact value is not as well defined.
The risk of contamination by serum thyroglobulin during fine needle puncture in causing a raised FNA thyroglobulin is minimal (less than 5%).
Anaplastic thyroid cancer, medullary thyroid cancer and de-differentiation of papillary thyroid cancer can produce "falsely" low FNA thyroglobulin levels. High serum anti-thyroglobulin antibody levels can interfere with FNA thyroglobulin measurements and result in a falsely low result.
References:
1. European Thyroid Association guidelines for cervical ultrasound scan and ultrasound-guided techniques in the postoperative management of patients with thyroid cancer. Leenhardt L et al. Eur Thyroid J 2013; 2:147-159
2. Significance of low levels of thyroglobulin in fine needle aspirates from cervical lymph nodes of patients with a history of differentiated thyroid cancer. Borel A-L et al. Eur J Endocrinol 2008; 158:691-698
3. Any detectable thyroglobulin in lymph node biopsy washouts suggests local recurrence in differentiated thyroid cancer. Yap N S-J et al. Endocrine Connections 2014; 3: 150-155
4. Thyroglobulin in lymph node fine-needle aspiration washout: a systematic review and meta-analysis of diagnostic accuracy. Grani G et al. JCEM 2014; 99(6): 1970-1982
5. Thyroglobulin in washout fluid from lymph node fine-needle aspiration biopsy in papillary thyroid cancer: large-scale validation of the cut off value to determine malignancy and evaluation of discrepant results. Moon JH et al. JCEM 2013; 98:1061-8