Vitamin D testing should not be done by routine screening but should be used only in people with clear signs of deficiency, or who are at risk for deficiency, for whom treatment is likely to be of benefit, according to a position statement from the Royal College of Pathologists of Australasia.

The statement recommends that vitamin D should be measured as 25-hydroxyvitamin D (25OH-D) and argues that an assay that measures only 25OH-D3 is sufficient for use in Australia and New Zealand. Patients should be monitored by the same laboratory after treatment because vitamin D assays vary.

After reviewing available scientific literature, a working party from the College advised against routine screening for vitamin D deficiency in adults (including pregnant women), healthy infants, and children. “As the main source of vitamin D is UVB sunlight exposure, vitamin D levels are correlated with time spent outdoors, exercise, and other aspects of a healthy lifestyle including bodyweight”, says Professor Yee Khong, President of the College.

The working group believes that testing healthy individuals would identify a substantial subgroup of patients with low 25OH-D concentrations, who would then be given treatment and repeat testing, without evidence that they would benefit from vitamin D supplementation. Khong warns, “The quality of evidence for health benefits of an adequate vitamin D status is highly variable and trials to improve this evidence are underway”.

William Fraser (University of East Anglia, Norwich, UK), believes that the statement is useful, but he cautions that it is based on the situation in Australia and New Zealand. “Some of the broad statements made would not be applicable in other countries throughout the world. The recent guideline published by the National Osteoporosis Society is much more applicable in the UK and other countries where vitamin D2 is present in the food chain, is freely available as a supplement, or is used as a prescribed medication.”

The Australasian group suggests that the target concentration for serum 25OH-D should be greater than 50 nmol/L at the end of winter. Serum 25OH-D concentrations should be retested no earlier than 3 months after commencement of supplementation with vitamin D. Once a desirable target has been achieved, no further testing is needed unless risk factors change.

Fraser questions the recommendation to measure only 25OH-D3 when the statement notes that D2 supplementation could be being used by some individuals tested. “It is a relatively short time since Australia moved from prescribing D2supplementation to D3 supplementation, and I am left wondering if D2 is totally absent from the food and supplement chain.”

Source: Lancet