Biotin, also known as the "beauty vitamin" has been shown to improve hair, skin and nails. But experts warn this supplement may come with a concerning downside. Mounting research shows high doses of biotin can interfere with common, diagnostic lab tests, making it more difficult for doctors to read results.In turn, that could put some patients at risk for mistreatment or misdiagnosis."Over the last 18 months, the number of cases that have reported biotin interference in the literature has increased dramatically," said Dr. Dana Stern, of the American Academy of Dermatology.The FDA has also seen an increase in the number of reported adverse events, including one death, related to biotin interference. The agency has issued a safety alert.Many documented cases are specific to thyroid testing, but experts warn everything from hormone tests to cancer screenings might be impacted.That's because many medical tests contain biotin themselves, and the combination can skew certain lab results as falsely positive or negative.Dr. Stern explained the interference can affect "even things like cardiac enzymes, which can measure whether a person is having a heart attack in an acute setting."So far, studies have shown that interference occurs at biotin doses of 10,000 micrograms and higher, but it's important to check if you're taking a multi-vitamin as well."A lot of patients don't necessarily realize that they're getting biotin from multiple supplement sources," said Dr. Stern.If you're taking biotin, either as a standalone supplement or as part of a multivitamin, let your doctor know and if you're getting any lab tests done, make sure you stop taking it in time. "The consensus is that you should stop taking biotin 48 hours to one week prior to having your laboratory results," Stern said.And while biotin is also found in foods such as cauliflower, almonds and eggs, experts say normal dietary intake doesn't cause interference.