Understanding supplements affecting blood test results is essential to getting accurate readings. Some common supplements can alter laboratory measurements, depending on the assay used and the context of the test. This page highlights which supplements may influence results and what to do before testing, with timing tips, safety guidance, and strategies to help ensure accuracy. Biotin is a frequently cited example of interference in certain immunoassays, which can lead to falsely high or low results in some tests. Iron and calcium supplements can affect hematology results or mineral studies, while high-dose omega-3s or vitamin C may influence lipid or glucose-related measurements in some scenarios. A range of herbal products—such as garlic, ginkgo biloba, or St. John’s wort—has also been associated with changes in specific test outcomes depending on the method used. Because interference patterns vary by laboratory technique, it is important to disclose every supplement you are taking, including dosages and brand names. Timing tips: coordinate with your clinician about which tests you will have and how to time any supplement dosing. You may be advised to pause certain supplements for a period before the blood draw; the exact pause depends on the test and dose. If possible, avoid taking the supplement on the day of collection, and always follow the lab’s preparation instructions and your provider’s guidance. When in doubt, document all products and ask for testing guidance rather than making assumptions. Safety and accuracy: keep an up-to-date list of all supplements and share it with your clinician or the testing site before the draw. Do not stop medications or supplements without professional guidance, especially if you rely on them for other health reasons. Bring the list to the appointment or include it with your test order to help ensure accurate results. If results seem inconsistent, discuss them with the provider and consider a retest if recommended.
