Before your blood test
Does biotin affect blood test results?
Short answer
Yes, and seriously. High-dose biotin (common in hair, skin and nail supplements) interferes with many immunoassays, producing falsely high or falsely low results for thyroid tests, troponin, hormones and vitamin D. The FDA has warned about it. Stop biotin at least 72 hours before a draw unless a clinician advises otherwise.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
Which results does it affect?
| Marker | Direction | How long | What to do |
|---|---|---|---|
| TSH | falsely lowers | Until biotin clears — 2–3 days after the last high dose | Stop biotin ≥72 hours before the draw [source] |
| Free T4, Free T3, total T4/T3 | falsely raises | 2–3 days | Stop biotin ≥72 hours before the draw [source] |
| Troponin (heart attack marker) | falsely lowers | 2–3 days | Tell emergency staff if you take biotin [source] |
| Vitamin D (25-OH) | falsely raises | 2–3 days | Stop biotin ≥72 hours before the draw [source] |
| Hormones on biotin-streptavidin assays (testosterone, estradiol, PTH, hCG, others) | raises or lowers | 2–3 days | Stop biotin ≥72 hours; tell the lab if you can't [source] |
Why does biotin interfere?
Many lab assays use a biotin-streptavidin bond to capture the molecule being measured. When there is excess biotin in the blood from supplements, it competes for those binding sites and the machine misreads the result — low for some assay designs, high for others. The pattern can look exactly like hyperthyroidism (low TSH, high free T4), and the FDA's safety communication describes a death from a falsely low troponin.
Typical multivitamins contain 30–100 micrograms of biotin and don't cause problems. The issue is 5,000–10,000 microgram 'hair, skin and nails' products, which are 50 to 300 times the recommended intake.
What to do before your draw
Stop biotin supplements at least 72 hours before a blood draw (some labs advise a week for very high doses). If you can't stop — some neurological conditions use prescription high-dose biotin — tell your clinician so an interference-free method can be requested. If a thyroid or hormone result looks impossible given how you feel, biotin is the first thing to ask about.
Common questions
How long should I stop biotin before a thyroid test?
At least 72 hours; a week if your supplement is 10,000 mcg or more. Biotin is water-soluble and clears quickly once stopped.
Does the biotin in my multivitamin matter?
Usually not. Interference is a high-dose problem (thousands of micrograms), not a multivitamin problem.
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.