What Is a Vitamin D 25-Hydroxy Test?
The 25-hydroxyvitamin D (25-OH D) test measures the storage form of vitamin D — the best indicator of vitamin D status.
Why 25-OH D?
- Has a long half-life (2–3 weeks)
- Reflects vitamin D from sun, food, and supplements
- Not affected by short-term fluctuations
Reference Ranges
- Severe deficiency: below 12 ng/mL
- Deficiency: 12–20
- Insufficiency: 20–30
- Sufficient: 30–50
- Toxic: above 100
How to Interpret
- Many clinicians target 40–60 ng/mL
- If deficient, supplement and recheck in 8–12 weeks
- Don't supplement without testing — excess is harmful
Source: NLM MedlinePlus, AACC.
Ratings summarize government-reported measures — they don't capture your personal needs. Visit the facility, ask about staffing and services, and use CMS checklists. This profile is informational only and is not a recommendation.
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