Vitamin D testing

At a time of increasing concern about low vitamin D levels in the world’s population and increased use of blood tests for the vitamin, scientists are reporting development of a much-needed reference material to assure that measurements of vitamin D levels are accurate. The report appears in the American Chemical Society’s journal Analytical Chemistry.

Karen Phinney and colleagues explain that medical research suggests vitamin D deficiency or insufficiency may be even more common than previously thought and a risk factor for more than just bone diseases. Low levels of vitamin D have been linked to the development of several conditions, including rickets (soft and deformed bones), osteoporosis, some cancers, multiple sclerosis and Parkinson’s disease.

People can make their own vitamin D simply by rolling up their shirt sleeves and exposing their skin to sunlight. But for those cooped up in offices all day long, food and dietary supplements also can provide vitamin D. With this renewed interest in vitamin D, scientists need an accurate way to measure its levels in the blood.

Measuring vitamin D itself doesn’t work because it is rapidly changed into another form in the liver. That’s why current methods detect levels of a vitamin D metabolite called 25(OH)D. However, the test methods don’t always agree and produce different results. To help laboratories come up with consistent and accurate methods, the researchers developed a Standard Reference Material called SRM 972, the first certified reference material for the determination of the metabolite in human serum (a component of blood).

The researchers developed four versions of the standard, with different levels of the vitamin D metabolites 25(OH)D2 and 25(OH)D3 in human serum. They also determined the levels of 3-epi-25(OH)D in the adult human serum samples. Surprisingly, they found that this metabolite - previously thought to only exist in the blood of infants - was present in adult serum. “This reference material provides a mechanism to ensure measurement accuracy and comparability and represents a first step toward standardisation of 25(OH)D measurements,” say the researchers.

The authors acknowledge funding from the National Institutes of Health, Office of Dietary Supplements.