MAYWOOD, Il. -- Blood tests to measure vitamin D deficiency are among the most frequently ordered tests in medicine.
But a Loyola University Chicago Stritch School of Medicine study of two new vitamin D tests found the kits are inaccurate in many cases. Earle W. Holmes, PhD, presented findings at ENDO 2012, the 94th Annual Meeting and Expo in Houston.
Holmes and colleagues examined how well the two new tests, Abbott Architect and Siemans Centaur2, performed on 163 randomly selected blood samples. In 40 percent of the Abbott Architect specimens and 48 percent of the Siemans Centaur2 specimens, results were at least 25 percent too high or 25 percent too low. (The maximum recommended total allowable error is plus-or-minus 25 percent.)
"There has been an exponential increase in the number of vitamin D tests ordered for patients," Holmes said. "But our study of two newly approved tests showed they had pretty poor performance."
The study by Holmes and colleagues included 163 specimens -- 123 from women (median age 54) and 40 from men (median age 59). Researchers used the two new test kits on the specimens, and compared results with findings from a gold standard method called LCMS, which has been shown to provide accurate vitamin D measurements. (LCMS stands for liquid chromatography/tandem mass spectrometry.)
The new tests tended to overestimate vitamin D deficiency. According to the LCMS measurements, 33 of the 163 specimens showed vitamin D deficiency. But the Abbott test showed that 45 specimens had vitamin D deficiency and the Siemens test showed that 71 subjects had vitamin D deficiency. Such inaccuracies could lead to overtreatment of vitamin D deficiency, Holmes said.
Holmes said inaccurate test results could lead to misdiagnoses of patients and confound efforts of physicians, nutritionists and researchers to identify the optimal levels of vitamin D for good health.
People get vitamin D from their diet, from exposure to the sun and from supplements. Vitamin D aids in the absorption of calcium, which is needed for strong bones. Vitamin D helps increase bone density and decrease fractures. Recent studies have found vitamin D also may decrease the risk of osteoporosis, high blood pressure, cancer, heart disease and diabetes.
Populations that may be at high risk for vitamin D deficiency include the elderly, people who are obese, babies who are exclusively breast fed and people who don't get enough sun.
Holmes is a professor in the departments of Pathology and Molecular Pharmacology and Therapeutics of Loyola University Chicago Stritch School of Medicine. Other co-authors of the study, both at Loyola, are Jean Garbincius, BA, and Kathleen McKenna, MBA.