I am reprinting here an email I received from John Cannell, MD.
The New York Times just posted their article (Jan. 7 2009) about Quest Diagnostic Laboratory's recall of their vitamin D blood tests. To my knowledge, this is the biggest recall in the history of medicine. http://www.nytimes.com/2009/01/08/business/08labtest.html?emc=eta1
It is important to note that I think Quest Diagnostics has fixed the main problem with their vitamin D testing. As far as I can tell, the problem was in their preparation of blood samples.
However, I cannot get Quest to fix their second problem, correlating their method with the method used in virtually all the major scientific studies of vitamin D, the DiaSorin RIA (I am a consultant for DiaSorin). When you read that levels of 50 ng/ml protect you from heart disease, that does not mean levels of 50 by Quest, rather levels of 50 by a method correlated with DiaSorin RIA.
So don't be afraid to use Quest, but, if you do use Quest, you must divide your 25(OH)D result by 1.3 to get an accurate 25-hudroxy-vitamin D [25(OH)D]. Thus, if Quest says your 25(OH)D is 40 ng/ml, divide 40 by 1.3 (40/1.3 = 30) to get a true reading of 30 ng/ml.
As a 25(OH)D level of 50 ng/ml is the minimum needed for good health, your Quest level must say 65 ng/ml or higher for optimum health (65/1.3 = 50). Thus, when you read that levels of 50 ng/ml protect you from breast cancer that would be levels of 65 ng/ml if you use Quest.
LabCorp is not affected by this recall and continues to have accurate vitamin D tests, correlated very well with DiaSorin RIA.
Remember, you can save money by starting vitamin D supplements before getting your 25(OH)D tested. Most adults need 5,000 IU per day of vitamin D in the winter. Children need about 1,000 IU per every 25 pounds of body weight. However, many people will still be deficient at these doses so after taking the vitamin D for three months, get tested.
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