Biotin (vitamin B7)
Water-soluble B vitamin that can interfere with many lab immunoassays at high doses
Also known as
Definition
Biotin (vitamin B7) is a water-soluble B vitamin the body needs for growth, for breaking down and using food and for making fatty acids. Excess amounts leave the body in the urine. Biotin is found in foods such as egg yolk, organ meats, legumes, nuts and milk. For lab results it matters mainly because high-dose supplements can distort many immunoassays.
| Parameter | Value |
|---|---|
| Reference Range | No uniform reference range: for some B vitamins it is not clear what a normal level is, and labs use different ranges. The reference range on your own report is what counts; discuss it with your doctor. |
Agree on your personal target range with your doctor.
↓ What a low value means
Biotin deficiency can come with skin rashes, hair loss, brittle nails, muscle pain and a swollen tongue. Low B vitamin levels can be linked to alcohol use disorder, celiac disease, Crohn's disease, other malabsorption conditions, surgery on the digestive tract or certain medicines. The values are hard to interpret because inflammation and medicines also affect them; discuss your result with your doctor.
↑ What a high value means
High biotin levels usually come from supplements. No toxic symptoms from biotin are known; that does not make high amounts free of consequences, because they can distort lab results. High B vitamin levels can also be linked to conditions such as liver disease. About the measurement effect: many immunoassays rely on a streptavidin-biotin bond. Biotin from supplements can interfere with these tests and, depending on test design, produce falsely high or falsely low results, for example for TSH, fT4, total T3 and thyroglobulin. In one study with high-dose biotin, interference peaked two hours after intake.
When to test
A vitamin B test is mainly ordered for symptoms that suggest a deficiency or when risk factors are present. It is measured in blood or urine; fasting may be needed before a blood sample. More relevant for most people: if you take biotin, tell your doctor and the lab before every blood draw. Whether and for how long to leave it out beforehand is something to clarify with them.
Frequently asked questions
Which lab values can biotin distort? +
Immunoassays based on a streptavidin-biotin bond are affected. This has been described for TSH, fT4, fT3, total T3, thyroglobulin and other hormone tests, as well as for tests used when heart muscle damage is suspected. Which tests are affected in your lab depends on the analyzer.
Do I need to stop biotin before a blood draw? +
Clarify this with your doctor. Expert articles advise considering biotin as a possible cause when a lab value does not fit the clinical picture. So before every blood draw, say whether and how much biotin you take, even if it is part of a combination product.
Is too much biotin harmful? +
No toxic symptoms from biotin are known; excess amounts leave the body in the urine. That does not make high amounts harmless: they can interfere with lab tests and lead to misleading results and misinterpretation. Whether a supplement is right for you is something to discuss with your doctor.
Where does the body get biotin from? +
Biotin is found in many foods rich in B vitamins, for example egg yolk, organ meats such as liver and kidney, legumes, nuts, milk, cereal, pork and yeast.
Biotin (vitamin B7)
Sources
- MedlinePlus, National Library of Medicine: Vitamin B Test
- MedlinePlus, National Library of Medicine: Pantothenic acid and biotin
- Samarasinghe S et al. – Biotin interference with routine clinical immunoassays, Endocr Pract 2017 (PMID 28534685)
- Ylli D et al. – Biotin Interference in Assays for Thyroid Hormones, Thyrotropin and Thyroglobulin, Thyroid 2021 (PMID 34042535)
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.