A Different Kind of Interaction
Most people think of supplement risks in terms of drug interactions. But supplements can also interfere with the laboratory tests used to diagnose and monitor conditions — skewing the numbers themselves, even when the supplement isn't interacting with a medication. The clearest, best-documented example is biotin.
Why Biotin Throws Off Tests
Many common lab tests use biotin–streptavidin technology to detect and measure substances. When someone takes high-dose biotin (often sold for hair, skin, and nails at doses far above the 30 mcg adult Adequate Intake), the extra biotin can interfere with these assays. As the NIH Office of Dietary Supplements explains, 'very high intakes of biotin may interfere with diagnostic assays that use biotin–streptavidin technology and are commonly used to measure levels of hormones (such as thyroid hormone)' [1].
Tests that can be affected include [1]:
- Thyroid tests (including TSH) — results can mimic or mask a thyroid problem
- Hormone immunoassays generally
- 25-hydroxyvitamin D
- Troponin (a cardiac marker)
- NT-proBNP (a heart-failure marker)
Depending on the test, biotin can push a result falsely high or falsely low. NIH notes that the FDA advises health care providers 'to ask their patients about any supplements they may be taking that contain biotin and to consider biotin interference as a possible source of error if laboratory test results do not match the clinical presentation' [1]. The stakes can be serious: per NIH, a patient with high biotin intake died after a troponin test gave a falsely low result due to biotin interference [1].
Other Supplements Worth Mentioning
Biotin is the standout, but it isn't the only one. For example, high-dose vitamin C can affect some blood-glucose meters and stool occult-blood tests. The practical lesson is the same for all of them: the lab and your clinician need to know what you take.
What to Do
- Tell your clinician and the lab about every supplement and dose — especially biotin — before testing.
- Ask whether to pause biotin (commonly for a couple of days) before affected tests; follow your clinician's guidance.
- If a result doesn't fit how you feel, mention your supplements as a possible cause before acting on the number.
This is about accurate diagnosis, not drug safety — but it's exactly why 'tell your provider what you take' is more than a formality.