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Vitamin D blood test: Past and present debates, difficulties, and developments

Most people do not know of the problems that exist in accurately measuring vitamin D levels. If they had their blood drawn five times on the same day, they may well get back five different 25(OH)D levels, and the differences could be significant.

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About John Cannell, MD

Dr. John Cannell is founder of the Vitamin D Council. He has written many peer-reviewed papers on vitamin D and speaks frequently across the United States on the subject. Dr. Cannell holds an M.D. and has served the medical field as a general practitioner, emergency physician, and psychiatrist.

4 Responses to Vitamin D blood test: Past and present debates, difficulties, and developments

  1. Lynn says:

    Has anyone looked at the effect of supplementation timing in relation to test results? I have started having my patients hold their supplemental vitamin D the day of a blood draw, just in case the dose might falsely elevate their blood levels.

  2. The half life of 25(OH)D is so long and conversion in the liver is so quick that it does not matter if someone takes D that day of the blood test or not.


  3. JBG says:

    Progress in 25(OH)D testing has larger potential importance. It is hard to imagine anything that would cause interest in vitamin D to grow as dramatically as a 25(OH)D test as straightforward and cheap as the self blood test used by diabetics.

  4. Rita and Misty says:


    I agree with you regarding a self-blood test similar to one used by diabetics…and I think we’ll soon see a 25(OH)D like this…

    However, I think that the 25(OH)D test should be made a standard test, administered as part of one’s yearly physical….IMO–this would certainly cause interest in Vitamin D to increase dramatically.

    Also it would help if the medical community would STOP referring to D as a Vitamin, and rather called what it is: A Pro-Hormone….

    AGAIN: D is a pro-hormone, not a vitamin….

    Just my opinions…

    Rita :)

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