Vitamin D (25-OH)

This test measures your vitamin D status by quantifying 25-hydroxyvitamin D (25-OH-VD), the main circulating form of vitamin D and the accepted gold-standard marker for assessing overall vitamin D adequacy. It is suitable for anyone concerned about low vitamin D, including those with limited sun exposure, darker skin tones, older adults, people who are overweight or obese, and individuals with conditions affecting fat absorption such as coeliac disease, Crohn's disease, or cystic fibrosis. It is also useful for monitoring supplementation and for investigating symptoms such as bone pain, muscle weakness, or recurrent infections.

Vitamin D is essential for calcium and phosphate regulation, bone mineralisation, muscle function, and immune health. Deficiency is common in the UK, particularly during autumn and winter, and can contribute to rickets in children, osteomalacia in adults, and increased fracture risk. Low levels have also been associated with fatigue, low mood, and impaired immune defence.

Vitamin D Status
- 25-hydroxyvitamin D (25-OH-VD): the primary circulating metabolite used to assess vitamin D sufficiency, insufficiency, or deficiency.

Why it matters
Vitamin D deficiency is widespread yet easily overlooked because symptoms can be vague or absent. Identifying a low level allows timely correction through supplementation and lifestyle measures, supporting bone strength, muscle performance, immune resilience, and overall wellbeing. For those already taking vitamin D, testing confirms whether the dose is adequate or needs adjustment.