Abstract
Introduction: Thyroid conditions are among the most common endocrine disorders. Diagnosis is dependent on interpretation of laboratory tests. The challenge comes when the clinical picture is discordant with laboratory results.
Case Report: Patient is a 53-year-old male with history of cardiac transplantation, type 2 diabetes mellitus, history of amiodarone-induced hyperthyroidism. He was noted to have labs indicative of hyperthyroidism, while taking amiodarone, in 2016-2017, which was treated with methimazole. He was then noted to have abnormal thyroid function tests with low TSH to 0.3 IU/L, normal T3 and normal T4 levels. Thyroid stimulating immunoglobulin had been checked multiple times, and was normal, which is inconsistent with Graves’ disease. Prior radioactive iodine uptake scan, while off amiodarone, was noted to be normal. He was also scheduled for thyroidectomy at another hospital, which was cancelled due to normalization of thyroid function tests. Consultation was received for suppressed TSH to 0.323 IU/L, without symptoms of hyperthyroidism. He had been taking biotin during this time, which he subsequently stopped taking. Repeat TSH following discontinuation of biotin, was within normal range, most recent TSH 2.48 IU/L, free T4 1.03 ng/dL, free T3 2.7 pg/mL.
Discussion: Thyroid function tests are commonly ordered. Interpretation of these tests relies on the provider’s understanding of thyroid physiology in addition to interferences with medications and other conditions. High doses of biotin, which people take as supplements for multiple sclerosis, or metabolic disorders, or for healthy nails and hair, can cause thyroid function test abnormalities. Streptavidin and biotin are used in some immunoassay platforms to capture antigens (TSH, free T4) or antibodies. High levels of serum biotin can inhibit the formation of T4 antibody complex, which results in a falsely high free T4 result.
Conclusion: Thyroid Function tests should be interpreted very cautiously, especially in the setting of discordant clinical findings. Prior to ordering these tests, should attempt to obtain a detailed history of medications including over-the-counter supplements, which are commonly not reported during medication history.
References:Elston, Marianne S., et al. “Factitious Graves’ Disease Due to Biotin Immunoassay Interference—A Case and Review of the Literature.” The Journal of Clinical Endocrinology & Metabolism, vol. 101, no. 9, 30 June 2016, pp. 3251-3255., doi:10.1210/jc.2016-1971. Koehler, Viktoria F., et al. “Fake News? Biotin Interference in Thyroid Immunoassays.” Clinica Chimica Acta, vol. 484, 30 May 2018, pp. 320-322., doi:10.1016/j.cca.2018.05.053. Soh, Shui-Boon, and Tar-Choon Aw. “Laboratory Testing in Thyroid Conditions - Pitfalls and Clinical Utility.” Annals of Laboratory Medicine, vol. 39, no. 1, 13 Jan. 2019, pp. 3-14., doi:10.3343/alm.2019.39.1.3.
Natural History of Thyroid Function Tests over 5 Years in a Large Pediatric Cohort