Laboratory Test Reference Guide

Performed with every Thyroglobulin measurement to check for interference by Anti-thyroglobulin antibodies, causing false low results.

Thyroglobulin and Anti-Thyroglobulin

Thyroglobulin (Tg) is elevated in goitre, hyperthyroidism, inflammation or injury of thyroid and increases several fold during pregnancy and in newborns. Levels will be transiently elevated following thyroid surgery (2 months) and fine needle aspiration (3 weeks)

Tg is decreased in thyrotoxicosis factitia and thyroid agenesis

Tg is mainly used monitoring treatment in patients with well differentiated thyroid cancer.

Following surgery and radioiodine ablation of thyroid carcinoma, thyroglobulin is expected to become undetectable. Serum thyroglobulin can be used as a marker of recurrence, provided the tumour originally secreted thyroglobulin. See guideline (1) for additional information.

Anti-thyroglobulin antibodies (Anti-Tg) occur more frequently in patients with thyroid cancer than in the general population. (Anti-Tg) interferes with the Tg assay, causing false low Tg results. An anti-Tg level is measured and reported with all Tg requests.

Low Anti-Tg results are reported as < 22 IU/mL and are considered to be negative for significant interference”; when results ≥ 22 significant interference is probable.

Significant interference = Tg undetectable or <0.3 ug/L by sandwhich assay when RIA result is > 1ug/L.

Probability of significant interference (all percentages are approximate only)

Thyroid cancer patients                   

Anti Tg  < 22  = 2.5%                          

Anti Tg : 25    =  5%

Anti Tg: 40      = 10%

Anti Tg: 80      =  20%

Anti Tg: 1000  =  30%         

Interference as defined by Tg under–recovery (<75%) occurs in 80% of samples when  Anti-Tg is detected (> 22 IU/mL) and virtually all samples when Anti-Tg is 1000 IU/mL

1)    2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer.  Bryan R. Haugen,,* Erik K. Alexander, Keith C. Bible,Gerard M. Doherty, Susan J. Mandel, Yuri E. Nikiforov, Furio Pacini, Gregory W. Randolph, Anna M. Sawka, Martin Schlumberger,Kathryn G. Schuff, Steven I. Sherman, Julie Ann Sosa, David L. Steward, R. Michael Tuttle, and Leonard Wartofsky. THYROID Volume 26, Number 1, 2016. DOI: 10.1089/thy.2015.0020

2)    Serum Thyroglobulin (Tg) Monitoring of Patients with Differentiated Thyroid Cancer Using Sensitive (Second-Generation) Immunometric Assays Can Be Disrupted by False-Negative and False-Positive Serum Thyroglobulin Autoantibody. Carole Spencer,  Ivana Petrovic, Shireen Fatemi, and Jonathan LoPresti. . J Clin Endocrinol Metab. 2014 Dec; 99(12): 4589–4599.