lab interference
6 interactions related to lab interference
levothyroxine + biotin
Biotin (vitamin B7) does not interact with levothyroxine pharmacologically and does not change how the medication is absorbed or works. The issue is in the lab: high-dose biotin can interfere with the biotin-streptavidin immunoassays used to measure TSH, free T4, free T3, and thyroglobulin, which can produce a falsely low TSH and falsely high T4/T3 pattern that mimics an overactive thyroid and can prompt an inappropriate dose change.
biotin + troponin test
High-dose biotin (vitamin B7) can interfere with the biotin-streptavidin chemistry used in many cardiac troponin immunoassays, potentially producing a falsely low result. The FDA has warned about this since 2017, but real-world data suggest clinically meaningful interference is uncommon at the doses found in typical over-the-counter supplements. The practical risk is real but narrower than once feared.
vitamin c + glucose meter
Vitamin C (ascorbic acid) is a strong reducing agent that can interfere with the chemistry used by many fingerstick and bedside glucose meters, producing falsely high blood glucose readings. This is most likely with high-dose oral or intravenous vitamin C. Published case reports describe patients on high-dose IV vitamin C being misdiagnosed with diabetic ketoacidosis and given inappropriate insulin, leading to dangerous hypoglycemia.
vitamin c + stool occult blood test
Vitamin C (ascorbic acid) is a reducing agent that can block the guaiac peroxidase color reaction used in traditional guaiac-based fecal occult blood tests (gFOBT, including Hemoccult). This can produce a falsely negative result even when gastrointestinal bleeding is present, potentially masking a bleeding source. Newer fecal immunochemical tests (FIT) use antibodies to detect human hemoglobin and are not affected.
biotin + thyroid stimulating hormone test
High-dose biotin can interfere with the biotin-streptavidin immunoassays many labs use to measure TSH, free T4, free T3, and thyroglobulin. The result is a falsely low TSH alongside falsely elevated free thyroid hormones, a pattern that can mimic Graves' disease. Published case reports describe patients who were wrongly diagnosed with hyperthyroidism, and started on antithyroid drugs, because of biotin interference that resolved once biotin was stopped.
vitamin e + platelet function test
Higher-dose vitamin E (alpha-tocopherol) can inhibit platelet aggregation through a protein kinase C-dependent mechanism, prolonging bleeding times and producing abnormal results on platelet function tests such as the PFA-100, VerifyNow, and light transmission aggregometry. The effect is most pronounced alongside aspirin or other antiplatelet drugs and can complicate a workup for a suspected bleeding disorder.