Vitamin D, 25-Hydroxy
The main storage form of vitamin D and the best indicator of vitamin D status.
| Typical reference range | 30–100 ng/mL |
| Commonly cited optimal range | 40–60 ng/mL |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Vitamin D is made in the skin from UVB sunlight or obtained from food and supplements, then converted by the liver to 25-hydroxyvitamin D. The kidneys convert it further to the active hormone calcitriol, which controls calcium absorption.
Why it matters
Vitamin D is essential for calcium absorption and bone health and also influences muscle and immune function. Deficiency (below 20 ng/mL) causes bone softening and secondary hyperparathyroidism.
What a high result can mean
High levels almost always come from excessive supplementation; toxicity with high calcium is uncommon below 150 ng/mL.
What a low result can mean
Low levels are common with limited sun exposure, darker skin, higher latitudes and winter, obesity, older age, malabsorption (celiac disease, IBD, bariatric surgery), kidney or liver disease and certain medications (anticonvulsants, glucocorticoids).
What affects the result
No fasting required. Levels change slowly; recheck about 8-12 weeks after changing supplementation. Vitamin D3 raises levels more than D2. Expert opinions differ on the ideal target: 20 ng/mL (Institute of Medicine) versus 30 ng/mL or higher (Endocrine Society). Interpret with calcium and PTH.
Units and conversion
Usually reported in ng/mL.
- From nmol/L: multiply by 0.401 to get ng/mL
Also called on lab reports
Vitamin D, VITAMIN D,25-OH,TOTAL,IA, 25-OH Vitamin D, 25-Hydroxyvitamin D, Vitamin D 25-OH, Vitamin D, 25-OH, Total, 25(OH)D, Vitamin D, 25-Hydroxy, Total, 25-Hydroxy Vitamin D, Vitamin D, 25-OH, Total, LC/MS, Vitamin D 25 Hydroxy
Related tests: Vitamins & Nutrients
This page is educational and does not replace advice from a healthcare professional.