FDA recently posted a notice cautioning that biotin (Vitamin B7) supplements have potential to distort the results of certain lab tests. Some of the tests that can potentially be affected include the CA 19-9 and CEA tumor marker tests which are well known to our community.
Biotin in small amounts is contained in many multi-vitamins. It appears in larger amounts in multi-vitamins and supplements that are oriented to hair and nail health. The FDA notice notes the amounts of biotin supplementation that are high enough to potentially interfere with accurate test results. Avoiding such supplements in the days prior to your test is recommended. If you are taking multivitamins or supplements that may contain biotin, please take a look at the notice.
To find out if a certain blood test is affected by biotin, you can internet-search the test name together with biotin as a check.