Ask an expert: Can every day supplements interfere with my lab test results?

Researchers explain why it is crucial to keep your health care providers up to date on every pill and capsule you take.

With the rising popularity of vitamins and supplements in the health product market, it’s important to be aware of their effects. Vancouver Coastal Health pathologists Drs. Morris Pudek and Sophia Wong, who recently published a paper describing the impact of biotin on laboratory test results, emphasize that caution is needed when taking any supplement.

Q: Can over-the-counter vitamins or supplements, like biotin – which is marketed for hair and nail growth – actually cause harm?
Similar to many commonly available products, vitamins and supplements such as biotin do not always cause harm, but certainly have the potential to do so, particularly in unanticipated or unconventional ways.

Q: In what ways could vitamins or supplements interfere with medical tests?
Many clinical laboratory tests, such as those used in the diagnosis or monitoring of cardiac diseases, endocrine disorders, cancers, anemias and infectious diseases, could be adversely affected by the use of supplements.

For instance, if a patient has excess amounts of biotin present in their bloodstream, this can interfere with lab tests and lead to either falsely high or falsely low results. Biotin could also interfere with a blood test that helps to determine whether a patient has had a heart attack.

Another example would be creatine, which is a popular protein supplement used to increase muscle mass. An individual ingesting excess creatine may end up with an elevated creatinine test result, and may be mistaken to have kidney disease.

Q: So, just to be safe, should I stop taking all vitamins and supplements?
Not necessarily. Standard multivitamins are safe to ingest and generally do not have sufficient levels of anything that would cause issues with laboratory tests. The important thing is to let your health care provider know which vitamins and supplements you are taking, especially if you are taking high-dose formulations. In most cases and depending on the dose, skipping the vitamin or supplement one day to one week prior to getting tested is enough time to overcome any analytical issues. For others, alternative testing or a modified testing schedule may need to be arranged. Occasionally, the laboratory result may need to be interpreted differently. It really depends on the test and on the vitamin or supplement, so it is best to speak to your health care provider about it before you go in for any tests.

Q: How can I tell if supplements will interact poorly with my medications, affect my health condition or skew the results of a test?
It can be hard to know. There are hundreds of vitamins and supplements available commercially, with new products appearing on the market all the time, and their impact on a health condition, a medication or a laboratory result may not be readily apparent. The best rule of thumb is to tell your health care providers about any vitamin or supplement you are taking and ask about the possible effects.

Q: Is it true that I can’t overdose on vitamins or supplements?
This is actually a common misconception. While many vitamins are water-soluble and can be readily excreted by the kidneys, they can still cause toxicity. Some examples would be:

  • An excess of vitamin B6 (pyridoxine) can result in nerve damage. 
  • Vitamins A, D, E, and K, are fat-soluble and can accumulate in the body’s tissues to toxic levels. 
  • Vitamin D toxicity can occur from ingestion of megadoses of vitamin D supplements. 
  • Iron tablets may look like candy and are a common cause of poisoning in children, leading to acute gastrointestinal problems, coagulopathy and possible long-term liver disease. 

The benefits of large doses of vitamins or supplements have not been clearly demonstrated, so it is always important to review the dietary reference intake (DRI) and percent daily value (%DV) if available and talk to your health care provider about any questions or concerns you may have.

Dr. Morris Pudek is the regional medical discipline leader of clinical chemistry at Vancouver Coastal Health.
Dr. Sophia Wong is a medical biochemist and the regional medical lead of pre- and post-analysis for Vancouver Coastal Health and Providence Health Care Laboratories.


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