Not medically reviewed
Endocrine
25-hydroxyvitamin D (25(OH)D)
Not medically reviewed · Content last updated · 1 min read ·
This is the date the draft was written, not a medical review date.
The main circulating storage form of vitamin D, reflecting intake and skin synthesis over the preceding weeks. It is the accepted marker of vitamin D status, but the optimal threshold is debated.
Reference interval
| Conventional (ng/mL) | SI (nmol/L) | |
|---|---|---|
| Adults | 20–50 ng/mL | 50–125 nmol/L |
Specimen: Serum · Conventional × 2.496 = SI
Causes of high values
Excess supplementation (toxicity usually above about 150 ng/mL or 375 nmol/L), granulomatous disease that increases 1,25-dihydroxyvitamin D production, some forms of hypercalcaemia.
Causes of low values
Limited sun exposure, covering clothing and dark skin pigmentation, northern latitudes and winter, poor intake, malabsorption, obesity, chronic kidney and liver disease, enzyme-inducing drugs, breastfed infants without supplementation.
Pre-analytical and method notes
Several guidelines define deficiency as below 20 ng/mL (50 nmol/L) and insufficiency as 20 to 30 ng/mL (50 to 75 nmol/L), while others use lower thresholds, so the interval shown is illustrative. Assay agreement is imperfect, and seasonal variation is large in people with limited sun exposure. Reference intervals vary by laboratory, method and population; use the interval printed on the report.
References
- Williams Textbook of Endocrinology. Elsevier, 14th edition (2019) — Tier 3 (textbook)
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Loscalzo J, et al.. Harrison's Principles of Internal Medicine. McGraw-Hill, 21st edition (2022) — Tier 3 (textbook)
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