A 52-year-old woman with progressive multiple sclerosis despite treatment was started on biotin 300 mg per day, based on a recent phase 3 trial showing improvement of multiple sclerosis symptoms with high-dose biotin.
Laboratory test results
Stephanie L. Lee
Thyroid-stimulating hormone measured in November 2015 was low (< 0.006 uU/mL) during an evaluation for fatigue (see Table for all thyroid tests). Thyroid tests in January were normal. However, thyroid function testing in February became markedly abnormal.
The physical exam and thyroid ultrasound were normal. Other studies performed included a normal urinary iodine (130 µg per 24 hours), negative thyroperoxidase, thyroid-stimulating immunoglobulin and human anti-mouse antibodies (HAMA), and a normal thyroid ultrasound and nuclear thyroid scan with uptake (10% at 6 hours and 16% at 24 hours). Dilution did not demonstrate interference or hook effect (a falsely low test result because of an excess of antigen in a sandwich immunoassay).
A literature search found only an alert from the Endocrine Society newsletter in January describing abnormal thyroid studies from high-dose biotin. After holding biotin for 5 days, repeat thyroid tests normalized. After restarting biotin for 5 days, thyroid levels again became abnormal, confirming biotin interference.
This case illustrates serious interference with some thyroid immunoassay tests by high-dose biotin ingestion resulting in the false diagnosis of severe thyrotoxicosis. Excess biotin can cause misleading test results — low creatine phosphokinase in acute coronary syndrome, negative human chorionic gonadotropin in ectopic pregnancy, low adrenocorticotropic hormone and high cortisol in Addison’s crisis, low TSH and high free thyroxine in myxedema coma — profoundly affecting medical decision making. In this case, incongruity of normal total T4 with elevated free T4 and free triiodothyronine suggested a laboratory artifact sparing further consumption of health care resources.
Most hormones and biomolecules are measured with assays using target-specific antibodies. Some assays employ biotinylated antibody in a streptavidin “capture” system. Test results can be confusing unless the clinician knows the effects of biotin on the specific measurement method and that the patient takes supplemental biotin. Small molecules (eg, T4 and T3) might be measured with a competitive immunoassay with biotinylated antibodies, and streptavidin and excess biotin in this type of assay causes falsely high results (Figure). Excess biotin in sandwich immunoassays used for larger molecules, such as adrenocorticotropic hormone, intact parathyroid hormone and TSH, displace the biotinylated capture antibody from the biotin-streptavidin complex yielding falsely low measurements.
Biotin does not affect assays performed after dialysis or by liquid chromatography/mass spectrometry. Some laboratories advise patients to stop taking biotin 8 hours before testing, but the length of time biotin affects tests varies depending on the test and the biotin dose. Although the interference by a single ingestion of biotin 30 mg on the laboratory test for estradiol, dehydroepiandrosterone sulfate and testosterone resolved by 8 hours, the effects on free T4, free T3 and thyroglobulin tests did not return to baseline after more than 25 hours.
Additional research must delineate the dose and time dependence of biotin interference with commonly used immunoassays. Clinicians and laboratories should appreciate potential interference in some immunoassays and that artifactual data may result in incorrect diagnosis and treatment. Biotin may result in a falsely low TSH and elevated free T4 and free T3 in biotin-containing immunoassays. As demonstrated in three recent studies, the clinician may erroneously diagnose hyperthyroidism unresponsive to antithyroid medications and harm patients by referring them for either radioactive iodine ablation or surgery to definitively treat the “hyperthyroidism.”
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Stephanie L. Lee, MD, PhD, ECNU, is an Endocrine Today Editorial Board member. She is associate professor of medicine and director of thyroid health in the Section of Endocrinology, Diabetes and Nutrition at Boston Medical Center. She can be reached at Boston Medical Center, 88 E. Newton St., Boston, MA 02118; email: firstname.lastname@example.org.
James Robert Brennan, MD, FACE, is an endocrinologist in private practice at Laurel Endocrine and Thyroid Specialists in Columbia, South Carolina. He can be reached at email@example.com.
Disclosure: Brennan and Lee report no relevant financial disclosures.