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Vitamin & Supplements to Stop Before Blood Tests

Answer:

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 and other 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)
  • Tests for glucose, bilirubin, hemoglobin, calcium, chloride, and magnesium
  • Certain COVID-19 tests
  • Troponin tests used to help diagnose heart attacks
  • Hydroxyproline tests (for osteoporosis and other bone diseases)
  • Bone density scans
  • MRIs (magnetic resonance imaging)
  • 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. High-dose N-acetyl cysteine (NAC) may also interfere with certain tests, although this may depend on how it is administered.

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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38 Comments

Monica C
November 27, 2024

I discovered that a glucosamine supplement I was taking was causing alarming liver enzyme test results. Multiple tests, even an endoscopy and biopsy showed no problems. I stopped the glucosamine and test results dropped down to normal. I also found some data about the effect.

ConsumerLab.com
December 01, 2024

You can find information about this in the Concerns and Cautions section of our Joint Health Supplements Review https://www.consumerlab.com/reviews/review-glucosamine-chondroitin-msm-boswellia-supplements/jointsupplements/#glucosamine-liver-toxicity.

Jude :-)
September 11, 2024

Wow, never had been advised about any of this prior 2 any of my lab tests, ever! Thank "U "

Sandra20630
September 10, 2024

Interesting, I'd just found this out on my own after having gone downhill for about 7 years, and with 2 years of worsening heart problems. I've been hypothyroid for many decades and was on a fair dose of a good thyroid medication but suspected my thyroid - so went investigating. What I discovered led me to pay out of pocket for ft3 ,ft4, and tsh labs after being off b vitamins for a week. Past tests had always shown high normal results, when in fact my test graph plummeted well below the whole chart for ft3 and 4 after removing the b vitamins that included biotin. Now, on the correct dose, my heart problems are resolving along with so many other things related to low thyroid. I told many friends who found that their doctors, and even endocrinologists, weren't aware of this! Many were on the wrong dose, it turned out. Anyone with thyroid issues knows how this will impact every facet of their lives. Hopefully the professionals will read this.

Mary22139
March 04, 2025

I experienced low free T3 and T4 with normal TSH taking 5 mg of biotin daily. I also experienced low T3 and T4 with normal TSH taking 168 mg elemental sustained release magnesium at night. In both cases, values returned to normal after stopping these two supplements. I am hoping I can resume taking the magnesium earlier in the day.

ConsumerLab.com
March 11, 2025

See our article about supplements that may interfere with thyroid medication https://www.consumerlab.com/answers/do-any-supplements-interfere-with-thyroid-hormones/hypothyroidism-and-supplements/.

Mary19288
April 14, 2024

Thanks, ConsumerLab!! And this... is why I subscribe.

Marleina20636
September 10, 2024

I recently had blood work & my pcp had me stop taking magnesium (which did not make me happy). He said it interfered with my potassium. I have tried researching this w/o much luck.

ConsumerLab.com
September 17, 2024

We are not aware of evidence indicating that magnesium influences laboratory measurements of potassium levels, but magnesium may affect levels of potassium levels in the body, as highlighted in our Potassium Supplements Review: https://www.consumerlab.com/reviews/potassium-supplements-review/potassium/#using-taking

Researcher
July 15, 2023

WoW! Thank you so much for this information! I had no idea. I just had a annual blood test and my thyroid was off. I do take supplements and am retesting in 6 weeks as my php said it was confusing relating to other results. I will also check back on here a month before blood work for additional info. THANK YOU! CONSUMER LAB!

ConsumerLab.com
July 17, 2023

Thank you for your kind words, we're glad you found the information helpful.

marlene17416
July 11, 2023

I was advised to stop fish oil, turmeric and vitamin e before a medical procedure because of bleeding risk. Surprised at the number of supplements’ cautions regarding tests and procedures. I now look up all my individual supps. before
Med tests.

terri17414
June 12, 2023

does taking collagen powder interfere with bone marker tests, particularly urine tests?

ConsumerLab.com
July 13, 2023

We've added information about this in the answer above, and more details can be found in the "Concerns and Cautions" section of our Collagen Supplements Review https://www.consumerlab.com/reviews/collagen-supplements-review-peptides-hydrolysate/collagen/#bone-tests.

Jada
June 02, 2023

Great information! Thanks

Laura47
March 23, 2023

Thank you… Very helpful post.

Researcher
February 21, 2023

THANK YOU SOOOO VERY MUCH. I had no idea.

ConsumerLab.com
February 12, 2023

Glad you found it helpful Sandra!

Sandra Collins
February 12, 2023

Thank you so much for that helpful info. My Dx’s never told me about any of this!

raymond17407
February 07, 2023

Don't forget about Red Yeast Rice or other "natural statin" supplements raising liver enzymes.

ConsumerLab.com
February 12, 2023

See the "Concerns and Cautions" section of our Red Yeast Rice Supplements Review for more about the potential effects of red yeast rice supplements on the liver https://www.consumerlab.com/reviews/red-yeast-rice-supplements-review/red-yeast-rice/#liver.

Maureen17406
February 07, 2023

I had no idea, thanks!

Marcella17405
February 07, 2023

Thanks for this info. I get a full body bone scan every 6 mos. and no one
at facility ever told me not to take calcium before test.

Tracy3333
February 07, 2023

thanks love hearing these kinds of info

ConsumerLab.com
February 07, 2023

You're welcome Tracy, glad to hear it's helpful!

Shelia17400
August 26, 2022

This information is very beneficial. Thank you!

Researcher
July 17, 2022

This is very helpful. I had no idea. It is an excellent and important reminder, that supplements in any form need to be discussed with your doctor. It is also important as WE must take steps to be informed on anything we ingest before having blood work.

Petr17394
July 10, 2022

Great

Joann17393
July 10, 2022

Thanks!

Judith17390
July 08, 2022

Many thanks

Cheryl17387
July 08, 2022

What an excellent review! Thank you Consumer Lab.

Sarafina17386
July 08, 2022

Thanks. Very helpful.

Linda17380
July 08, 2022

As a person who has frequent lab work, I find this very helpful. Thank you.

ConsumerLab.com
July 08, 2022

Thank you for your kind words Linda, we're glad to hear it's helpful for you!

Rattattat
July 08, 2022

I recently started taking Biotin to help with my hair. I am hypothyroid and when I took my thyroid blood test the result that came back was off the chart crazy . I had to go to an endocrinologist to find out about Biotin.
She said to discontinue for a week before any future tests, and if I had any visits to the ER always tell them that I take Biotin or the blood test results will make them think I'm having a heart attack.

raymond17378
February 07, 2023

Wow, good endo! I've got an endocrinologist neighbor who had NO IDEA what Reverse T3 is.

Sandra Collins
February 12, 2023

That is sad, but not surprising.

Danielle17376
June 02, 2023

Yes for me it is a week with no vitamins.

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