New vitamin D tests called inaccurate

Houston - Two new blood tests for vitamin D levels are inaccurate in at least 40 percent of laboratory specimens analyzed, according to results of a recent study.

A research team headed by Earle Holmes, Ph.D., professor of pathology and pharmacology, Loyola University Stritch School of Medicine, compared results of two new 25-hydroxyvitamin D immunoassay tests in 163 randomly selected blood samples, Newswise.com reports. The samples included 123 from women with a median age of 54, the remainder from men with a median age of 59. One test used a reagent kit and a lab-testing platform from Abbott Laboratories; the other used a reagent kit and platform from Siemens Healthcare Diagnostics. The researchers performed the tests in a Loyola laboratory following manufacturers’ instructions.

The same blood samples were then tested using liquid chromatography/tandem mass spectrometry. That test was performed by Quest Diagnostics.

Finally, researchers performed a statistical analysis of the results and found that in 40 percent of the Abbott-tested specimens and in 48 percent of the Siemens-tested specimens, the results were at least 25 percent too high or 25 percent too low when compared with the third technique. With the Siemens test, 71 of the 163 results indicated vitamin D deficiency; the Abbott results indicated vitamin D deficiency in 45 of the samples. The liquid chromatography/tandem mass spectrometry results indicated vitamin D deficiency in only 33 of the samples, the authors report in their abstract.

“Both of the immunoassays erred on the side of overestimating vitamin D deficiency, which could lead to overtreatment,” Dr. Holmes told Newswise.com.

The study was presented at the Endocrine Society’s 94th Annual Meeting, held in Houston in June.

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