Vitamin D (25-OH)

The storage form of vitamin D and the standard way status is assessed. In the UK it falls through autumn and winter for almost everyone, because the sun is not strong enough for the skin to make any between October and March.

Vitamin D in the Biomarker Guide — what it is, why it is tested, and what moves the number.

Add-on markers can only be added to venous samples.

Timing

No fasting needed and no particular time of day. The month matters far more than the hour. In the UK a level taken in March is close to your yearly low and one taken in September close to your peak.

Turnaround: the lab reports this test within 24 hours of receiving your sample, counted in working days. Most samples reach them within about 3 days of posting. Full detail on our Turnaround Times page.

We do not interpret results. Not medical advice or a diagnosis.