Test Summary

This test may help identify thyroid stimulating hormone (TSH) autoantibodies. When the serum TSH level is discordant with clinical manifestations or other test results (eg, markedly elevated TSH with normal free triiodothyronine and free thyroxine levels), this test may be used to determine if TSH autoantibodies are the cause of discordance.

TSH autoantibodies can bind TSH to form a macromolecule (macro-TSH) that has low biological activity but interferes with TSH immunoassays [1]. Interference by macro-TSH may be screened by polyethylene glycol precipitation and gel filtration chromatography [1].

Anomalous TSH levels may also be caused by a range of interfering substances, such as biotin, heterophilic antibodies, and antibodies to streptavidin and ruthenium [1].

Other conditions that may result in elevated TSH levels with normal free triiodothyronine and free thyroxine levels include subclinical hypothyroidism, poor adherence to (or malabsorption of) thyroxine therapy, certain drugs (eg, amiodarone), nonthyroidal illness recovery phase, and TSH resistance [2].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Favresse J, et al. Endocr Rev. 2018;39(5):830-850.
2. Gurnell M, et al. Clin Endocrinol (Oxf). 2011;74(6):673-678.

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