If you take biotin, tell the lab before you have blood drawn. Memorial Sloan Kettering Cancer Center reports that biotin, a B vitamin sold in hair and nail supplements, can interfere with some lab tests, including the cardiac troponin test, at amounts achievable with over-the-counter products.

Biotin is an essential vitamin that helps the body process sugar and fats, MSK says, and it is widely available in foods such as eggs, almonds, soybeans, peanuts and wholegrain cereals. Supplements come as pills, soft gels or gummies and are taken for skin, nail and hair health, but MSK says the evidence for hair growth or stronger nails is limited.

The cancer center says the vitamin is generally safe, but reports show it can throw off test results, mask disease states, overestimate a response to treatment or lead to unnecessary procedures. MSK cites a patient death linked to false low troponin results from high biotin intake, along with case reports of thyroid tests that returned to normal after the supplement was stopped. The FDA issued a safety communication on the problem in 2017, and MSK notes that newer-generation assays now prevent biotin interference for high-sensitivity troponin T and TSH testing.

Before any blood test, tell your doctor and the lab team about every supplement you take, including vitamins, herbs and home remedies, and ask whether any preparation is needed. MSK says that helps your providers manage your care and keep you safe.