Measuring vitamin D.

When assessing vitamin D status, measure serum 25-hydroxyvitamin D concentration as this reflects total body vitamin D reserves. Recent Australasian guidelines outline who should be tested for vitamin D deficiency, who should be treated and when repeat testing should be performed. A 25-hydroxyvitamin D threshold of at least 50 nanomol/L at the end of winter is a suitable treatment target. Measurement can be repeated after three months of repletion, and thereafter less frequently unless new risk factors for vitamin D deficiency arise. When interpreting vitamin D pathology reports, practitioners should be aware that some laboratories quote reference limits which are based on overseas rather than Australian guidelines.