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Vitamin & Supplements to Stop Before Blood Tests


There are a number of supplements that may interfere with blood, urine or stool tests, and even certain imaging tests. This can cause misleading results or lead to unnecessary additional testing or treatment.

More specifically, supplements can affect:

  • Thyroid hormone tests
  • Vitamin D and calcium tests
  • Prostate specific-antigen (PSA) tests
  • Tests for hepatitis B and hepatitis C
  • Tests of kidney function (blood levels of creatinine)
  • Certain COVID-19 tests
  • Troponin tests used to help diagnose heart attacks
  • Hydroxyproline tests (for osteoporosis and other bone diseases)
  • Bone density scans
  • Certain stool tests that may be used to screen for colon cancer and gastrointestinal bleeding
  • Pregnancy (hCG) tests
  • Anti-doping tests for athletes

The supplements that can cause these interactions include B vitamins such as biotin, niacin and riboflavin, as well as calcium supplements, creatine, iron supplements, St. John’s wort, vitamin C, L-tryptophan, and 5-HTP, as well as certain foods and drinks.

Sign in as a member to learn which vitamins and supplements interfere with which tests, when to stop taking these supplements before tests to avoid interference.

Be sure to tell your physician and laboratory about all the supplements you take, as interference may vary depending on the exact model of test used and can change when tests are updated or reformulated.

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