Limitations of Laboratory Testing

The Department of Laboratory Medicine strives to achieve high precision and accuracy in testing all specimens. However, all technologies have potential limitations and interferences that may lead to analytical variations that do not reflect a given patient's true physiological state. Whenever clinicians are concerned about test results that are unexpected and/or do not match clinical impressions, they are encouraged to contact laboratory personnel to discuss potential discrepancies.

Biotin Supplements

High doses of biotin (also known as vitamin B7) contained in nutritional supplements may interfere with immunoassays employing biotin as a reagent in the assay.

For testing through UW Medicine, biotin may cause falsely elevated values for the following tests:

• Thyroxine (Free) [T4FR]
• T3 (Free) [T3FR]
• Triiodothyronine (T3) [T3] (total T3)

In contrast, biotin may cause falsely low results for the following:

• thyroglobulin (typically ordered using Thyroglobulin and Thyroglobulin Antibody [THGLBN])
• Anti Thyroglobulin [ATG2]
• CA 19 9 [CA199]

Note that other common tests for thyroid function, Thyroid Stimulating Hormone [TSH] and Thyroxine (T4) [T4] (total T4), are NOT affected by biotin.

Biotin supplements of over 1 mg/d should be discontinued at least 24 hours before drawing blood for these tests, in order to assure that there is no interference. The daily recommended allowance for biotin is 0.03 mg and these biotin levels do not typically cause significant interference. However, supplements containing high biotin (vitamin B7) levels including those marketed for hair, skin, and nail benefits, may contain up to 20 mg of biotin, and physicians may recommend up to 300 mg per day for conditions such as multiple sclerosis. Biotin levels higher than the recommended daily allowance may cause significant interference with some lab tests, and the effect is different depending on the method used for testing.