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Vitamin D, 25-hydroxy (25-OH D)

Hormones & Fertility · also called Calcidiol, 25(OH)D

What it measures

25-hydroxyvitamin D is the main circulating form of vitamin D and the best measure of body stores. It is used to assess deficiency in bone disease, falls, malabsorption and abnormal calcium or PTH.

Specimen and preparation

Specimen: Serum or lithium-heparin plasma
Tube: Gold top
Preparation: Protect from light; no fasting needed.

Reference range

Group	Range
Deficient	<20 (<50) ng/mL (nmol/L)
Insufficient	20–29 (50–74) ng/mL (nmol/L)
Sufficient	30–100 (75–250) ng/mL (nmol/L)
Possible toxicity	>150 (>375) ng/mL (nmol/L)

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

Excess supplementation
Granulomatous disease (raises 1,25-OH D more)

Causes of low values

Limited sun exposure and dark skin or covered clothing
Malabsorption (coeliac, bariatric surgery)
Obesity
Chronic liver or kidney disease
Anticonvulsant drugs

Method

Chemiluminescent immunoassay or LC-MS/MS

Good to know

Use 1,25-dihydroxyvitamin D only in specific situations such as kidney failure or granulomatous disease. Thresholds for sufficiency differ between guidelines (20 or 30 ng/mL).

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