The Complex Web of Interferences With Thyroid Function Tests

Objective: Thyroid disorders are common. Serum thyroid stimulating hormone is frequently measured and is the single best initial biomarker to diagnose thyroid disease. Automated immunoassays used to evaluate thyroid function are susceptible to interferences that can affect test results and therefore clinical decisions. In this comprehensive review, our aim is to discuss common assay and drug interferences leading to abnormal thyroid function tests. Methods: Authors conducted a literature review of PubMed to include studies on drug related and laboratory assay interferences leading to primary and secondary thyroid dysfunction in addition to interferences with thyroid hormone replacement and thyroid function tests. Results: Overall, there are several assay interferences as well as drug interferences leading to primary thyroid dysfunction including iodine-containing drugs such as amiodarone, lithium, immune checkpoint inhibitors and tyrosine kinase inhibitors, drug interferences leading to secondary thyroid dysfunction such as glucocorticoids, and drug interferences affecting thyroid hormone absorption, metabolism, and thyroid binding globulin levels. In addition, assay interferences from biotin, heterophile antibodies, macro-thyrotropin or anti-streptavidin antibodies may occur without underlying thyroid dysfunction, leading to abnormal thyroid function tests. Conclusion: For appropriate patient management, it is imperative to identify assay interferences when discrepancies between clinical presentation and thyroid function test results are noted.