Can supplements interfere with diagnostic testing?

The short answer is yes they can. Certain nutrients in large amounts and if taken close to testing can interfere with blood tests, urinalysis, and even imaging results. This is concerning because of course we prefer testing to be as accurate as possible since it informs medical decisions. As NDs, it’s especially important to be aware of these potential interferences since we both recommend supplements and order blood work. We also play an integral role in educating our patients and communicating with other members of their healthcare team to improve overall health outcomes.

Biotin (B7) is a commonly used B vitamin found in multivitamins and hair, skin, and nail supplements. Biotin interference with diagnostic tests is a big one. The FDA has already stepped in and provided recommendations to help decrease potential interference by educating the public and by recommending that diagnostic test manufacturers design studies to test for biotin interference (1). Tests that are at risk of interference from biotin supplementation include hCG urine pregnancy tests, thyroid markers like TSH, T3, FT4, and troponin (2). The last of which is an important emergency marker that’s used to accurately diagnose acute MIs (heart attacks). These interferences are seen in patients taking upwards of 20 mg or greater of biotin per day, and the simple solution is taking lower doses of biotin and/or discontinuation 1-5 days prior to getting blood work done (2).

Folic acid (B9) supplementation can mask a B12 deficiency, which may not seem like a big deal but there can be serious consequences to not treating an underlying B12 deficiency quickly. Folic acid is a B vitamin which is important to supplement with during pregnancy, as it prevents neural tube defects in neonates. Folic acid and B12 are also both involved in the production of red blood cells (RBCs). Macrocytic megaloblastic anemia, or RBCs that are abnormally large and immature, result from a deficiency of either B vitamin which impairs the RBC's ability to circulate oxygen efficiently. On a blood test, your doctor would be able to tell if you were deficient in these vitamins based on the size of your RBCs, but folic acid supplementation can actually make the RBCs appear normal effectively masking an underlying B12 deficiency. Fortification with folic acid has been associated with higher rates of anemia and cognitive impairment in the elderly who have lower levels of B12, possibly due to masking or an increase in demand for B12 with folic acid excess (3). Either way, it’s typically recommended that folic acid not be supplemented in large amounts for very long or without the co-administration of B12 to prevent deficiency.

Vitamin C needs little introduction. It’s a popular nutrient that shows up in beauty supplements, cold remedies, and multivitamins. It has been used more and more frequently at high doses in various intravenous (IV) protocols; from cancer treatment to immune-boosting therapy. There is some concern that at these extremely high doses there may be some interference with glucose meter readings (4). This is a specific edge case, but an important one to be aware of since blood glucose needs to be tightly managed in diabetic patients on insulin and other diabetes medications. Oral vitamin C in a single dose of 1,000 mg or greater prior to urinalysis (UA) has also been shown to result in false-negative results for glucose, nitrites, bilirubin, leukocytes, and blood in the urine (5). This is certainly concerning, but avoiding vitamin C prior to UA is an easy solution.

Another nutrient that may affect imaging results is calcium. Calcium supplementation taken within 30 min of DXA scans for bone mineral density, especially of the lumbar vertebra, has been shown to skew results (6). Although the evidence is limited, riboflavin (B2) is another B vitamin that has reportedly affected UA results and drug tests. A trend in the research shows variability not just with different test types, but also between the manufacturers and specific testing technology used. As previously stated, an easy solution given the variability is to be aware of the potential for interference and avoid these supplements at least a few days prior to doing blood work, UA, or BMD testing.

Bottom line: regular supplementation is compatible with diagnostic testing, but because individual risk factors need to be accounted for it’s best to discuss your supplement routine with your doctor before continuing long-term.

Author: Emily Howard, ND, BSc


1. FDA reminds public of possible biotin interference for certain tests. U.S. Food and Drug Administration.,on%20the%20type%20of%20test. Accessed November 16, 2022.
2. Bowen R, Benavides R, Colón-Franco JM, et al. Best practices in mitigating the risk of biotin interference with laboratory testing. Clin Biochem. 2019;74:1-11. doi:10.1016/j.clinbiochem.2019.08.012
3. Mills J L, Molloy A M, Reynolds E H. Do the benefits of folic acid fortification outweigh the risk of masking vitamin B12 deficiency? BMJ 2018;360:k724. doi:10.1136/bmj.k724
4. Katzman BM, Kelley BR, Deobald GR, Myhre NK, Agger SA, Karon BS. Unintended Consequence of High-Dose Vitamin C Therapy for an Oncology Patient: Evaluation of Ascorbic Acid Interference With Three Hospital-Use Glucose Meters. J Diabetes Sci Technol. 2021;15(4):897-900. doi:10.1177/1932296820932186
5. Ko DH, Jeong TD, Kim S, et al. Influence of Vitamin C on Urine Dipstick Test Results. Ann Clin Lab Sci. 2015;45(4):391-395.
6. Krueger D, Checovich M, Gemar D, Wei X, Binkley N. Calcium supplement ingestion may alter lumbar spine bone mineral density measurement. J Clin Densitom. 2006;9(2):159-163. doi:10.1016/j.jocd.2006.01.002

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