"Pathologist Perspectives"

Quest Diagnostics Explains Confidence in LC-MS/MS Method

ONE ASPECT IN THE DEBATE about the integrity of Vitamin D tests produced by liquid chromatography–tandem mass spectrometry (LC 0150MS/MS) is the discussion about how this method can produce results that are significantly higher than those produced by immunoassay-based methods. Quest Diagnostics addressed this point directly.

In response to questions from THE DARK REPORT, Wael Antoine Salameh, M.D., Medical Director, Endocrinology at Quest Nichols Institute, located in San Juan Capistrano, California, provided a written reply. He wrote:

…we want to clarify four key facts to help you report these complex issues accurately.

First is that LC-MS/MS does not produce results with an upward “bias” relative to immunoassay techniques. This not a bias of LC-MS/MS; rather, the converse is true. Immunoassays tend to underreport Vitamin D2, skewing results lower for total Vitamin D levels.

Second, physicians who use Vitamin D2 therapy—which is the only form of therapy FDA approved for treating Vitamin D deficiency in the U.S.— therefore may not be able to accurately assess a patient’s Vitamin D2 levels using immunoassay techniques—possibly impeding effective therapy. Not surprising, NIST [National Institute of Standards and Technology], in developing reference materials for Vitamin D testing, has stated that “accurate assessment of Vitamin D status should include measurement of both hydroxylated forms (25-OH-D2 and 25-OH-D3).” Refer to: http://www.cstl.nist.gov/pro- jects/fy06/food0683904.pdf ). Quest Diagnostics’ Vitamin D test results (using LC-MS/MS) report separate results for Vitamin D2 and D3, as well as the total Vitamin D level, they comprise.

Third, as published literature demonstrates, results of immunoassays and LC- MS/MS correlate well for Vitamin D3, with minor variability. Keep in mind that Vitamin D2 can only be introduced into the body. Therefore, unless a person is undergoing Vitamin D2 therapy, a physician evaluating a patients’ Vitamin D level using results of different testing techniques can compare Vitamin D3 results from an LC-MS/MS test to the total Vitamin D level reported by an immunoassay test. Significantly, for the same reason, however, if a person is undergoing Vitamin D2 therapy, we believe strongly that the LC- MS/MS methodology will provide the clinician with a more meaningful Vitamin D profile because both Vitamin D2 and Vitamin D3 levels are measured.

To further emphasize this point, Salameh next wrote:

We also reject the notion that most published research on Vitamin D levels is based on a single type of testing technique providing a standard by which others should be based. Nor do we agree that our LC-MS/MS results would need to be correlated to results of other techniques in order to provide medically useful results. Again, we believe these notions are propagated largely by one or more individuals affiliated with one of our competitors… We stand by the LC– MS/MS method.

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