Skip to main content
Your session has expired. Reloading...
Vitamins

Vitamin D Blood Test

Vitamin D is a fat-soluble vitamin. Its main job is the absorption of calcium and phosphate from the gut. That makes it decisive for bone metabolism.

The skin produces it under the influence of sunlight. Food and supplements supply a smaller share.

Doctor's Assessment Included

When is this value abnormal?

See the value that applies to you:

Choose male or female — this range differs by sex.

Enter your age — this range changes with age.

This range also depends on context such as cycle phase or sample material; the highlighted rows apply to your group.

up to 69 years Your group

Decision limits per result, in nmol/l
Result Value (nmol/l)
Deficiency < 30
Sufficient ≥ 30

70 years and older Your group

Decision limits per result, in nmol/l
Result Value (nmol/l)
Severe deficiency < 35
Deficiency 35–50
Sufficient ≥ 50

Nederlandse richtlijnen zijn het niet eens over deze grens. Het Zorginstituut stelt vast: "Er ontbreekt een eenduidige grens voor vitamine D-deficiëntie" (2022). Wij volgen de Gezondheidsraad, het NHG en het Farmacotherapeutisch Kompas. De NVKC hanteert 50 nmol/l voor iedereen; de osteoporoserichtlijn hanteert 50 nmol/l bij verhoogd fractuurrisico.

Source: Gezondheidsraad Reference population: Nederlandse bevolking (Gezondheidsraad 2012)

Source: Zorginstituut Nederland Reference population: Nederlandse bevolking (Gezondheidsraad 2012)

Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.

Vitamin D (25-OH): what this test measures

This test measures 25-hydroxyvitamin D (25-OH-D) in the blood. That is the storage form of vitamin D. It is also the only form that says anything about your reserve. The result is reported in nmol/l.

25-OH-D has a half-life of two to three weeks. The result therefore reflects supply over the preceding months, not yesterday.

The active form is called 1,25-dihydroxyvitamin D. It is deliberately not measured. It has a half-life of hours and is tightly regulated by parathyroid hormone (PTH).

When stores run low, the body increases the conversion. The active value can then look normal, or even raised, while the reserve is empty. Ordering the 1,25 form for a suspected deficiency is the classic clinical mistake.

The report should give total 25-OH-D, meaning D2 plus D3. That matters for anyone taking a plant-derived D2 product. Some immunoassays under-recover D2.

Vitamin D (25-OH): why this value matters

Vitamin D governs the absorption of calcium and phosphate from the gut. That makes it decisive for bone metabolism. As the reserve falls, calcium absorption drops and PTH rises. The body then draws calcium out of bone to keep the blood level steady.

The Dutch Health Council does not use a laboratory reference interval here. It uses decision thresholds, and they differ by age.

25-OH-DUnder 7070 and over
Below 30 nmol/lDeficiencyDeficiency
30 to 50 nmol/lInsufficiencyDeficiency
50 to 75 nmol/lAdequate for bone maintenanceAdequate, but below the target where there is fall risk
Above 75 nmol/lNo demonstrated added benefitDesired in frail older people at risk of falls

The threshold shifts on your seventieth birthday. The same 40 nmol/l is called insufficiency in a forty-five-year-old. In a seventy-five-year-old that identical number is deficiency.

Above 75 nmol/l the evidence for hard clinical outcomes is limited. A higher number is not a target to chase.

The result is rarely judged alone. Calcium, phosphate and PTH belong with it. A low 25-OH-D alongside a raised PTH points to secondary hyperparathyroidism. That carries more clinical weight than the vitamin D figure by itself.

Vitamin D (25-OH): when is testing worthwhile?

Testing makes sense with complaints that fit a deficiency. Think of muscle weakness in the thighs, difficulty standing up, or bone pain.

Measuring can also be useful without complaints if a risk factor is known. Little daylight, darker skin, covering clothing, fat malabsorption or enzyme-inducing medication all count.

The month decides what you measure. A test in September shows the summer peak. A test in February or March shows the year's lowest point. If you want to compare two results, pick the same month.

Vitamin D (25-OH): symptoms of a high or low value

Low Levels

A low reserve causes no symptoms for a long time. When symptoms do appear, they are non-specific:

  • muscle weakness in the thighs and hip girdle
  • difficulty rising from a chair or climbing stairs
  • bone and muscle pain
  • an unsteady gait

Prolonged, deep deficiency produces osteomalacia in adults and rickets in children. Newly formed bone mineralises inadequately, causing bone pain and deformity.

In older people a low value is associated with muscle weakness and a higher risk of falling. That drives fracture risk further up.

These complaints fit dozens of other causes equally well. It is the number that prompts the conversation, not the symptom.

High Levels

A high 25-OH-D is almost always down to supplementation rather than sun. The skin throttles its own production once there is enough.

Toxicity with hypercalcaemia is generally not seen below roughly 250 nmol/l. It requires sustained very high intake.

There is a second cause that matters more clinically. Think of granulomatous disease such as sarcoidosis and tuberculosis. Some lymphomas belong here too.

Macrophages then convert 25-OH-D into the active form, outside the normal regulation. Hypercalcaemia can then occur at an entirely ordinary 25-OH-D.

That is why a raised calcium alongside vitamin D is a question for the GP. Not for the supplement shelf.

Vitamin D (25-OH): what to do about an abnormal value

Male

If Low

Low vitamin D may cause fatigue, muscle weakness, and bone pain. Consider 2000-5000 IU daily supplementation and increase sun exposure.

If High

High vitamin D may indicate excessive supplementation. Reduce supplement dose and retest in 3 months.

Female

If Low

Low vitamin D may cause fatigue, muscle weakness, and bone pain. Consider 2000-5000 IU daily supplementation and increase sun exposure.

If High

High vitamin D may indicate excessive supplementation. Reduce supplement dose and retest in 3 months.

Vitamin D (25-OH): lifestyle and this value

The Netherlands sits at roughly 52 degrees north. From October through March the sun is too low here. Too little UVB (290 to 315 nm) reaches the skin. Through those months there is effectively no endogenous production, and the body draws on its summer reserve.

The month of the blood draw is therefore part of the result. A March value is not comparable with a September value. A fall between the two is usually the season, not a deterioration.

A lower value is expected with:

  • darker skin, because melanin absorbs UVB and more exposure time is needed
  • covering clothing
  • indoor work and night shifts
  • obesity, because vitamin D is sequestered in adipose tissue
  • older age, because the skin holds less of the precursor
  • fat malabsorption
  • enzyme-inducing medication such as anticonvulsants and rifampicin
  • glucocorticoids, which accelerate breakdown

The Dutch Health Council advises certain groups to supplement:

  • people aged seventy and over
  • pregnant women
  • people with darker skin
  • people who get little daylight

What amount fits is a question for the GP or the Voedingscentrum.

Do you take high-dose biotin? Mention it when the sample is drawn. Biotin can interfere with some 25-OH-D immunoassays and push the result falsely high.

Vitamin D (25-OH): frequently asked questions

Why is there no reference interval for vitamin D?

Because no laboratory reference exists for it. The Dutch Health Council uses decision thresholds: below 30 nmol/l deficiency, 30 to 50 nmol/l insufficiency. From 50 nmol/l the value is adequate for bone maintenance. Labs may state their own limits.

Does the threshold change with age?

Yes. From seventy the line moves up and anything below 50 nmol/l counts as deficiency. Fall risk and fracture risk weigh more heavily at that age. Above 75 nmol/l is desired in frail older people at risk of falls.

Why does the lab not measure the active form?

The active form survives only hours and parathyroid hormone keeps it tightly controlled. When the reserve is empty the body steps the conversion up. The active value can then look normal while stores are gone. The storage form 25-OH-D therefore gives the honest picture.

Can a supplement distort the result?

A plant-based D2 product can, because not every immunoassay fully recognises D2. Ask for total 25-OH-D, meaning D2 and D3 together. High-dose biotin can also interfere with some assays. Mention it before the draw.

Test Products

This marker is included in the following test panels.

General checkup

General checkup

A broad blood test covering 18 values across liver, kidneys, thyroid, heart, vitamins and blood count.

ALT (Alanine Aminotransferase) GGT (Gamma-Glutamyl Transferase) Creatinine eGFR (Estimated Glomerular Filtration Rate) TSH (Thyroid Stimulating Hormone) Total Cholesterol HDL Cholesterol LDL Cholesterol Triglycerides Glucose (Fasting) Vitamin D (25-OH) Vitamin B12 Ferritin Hemoglobin Leukocytes (WBC) Platelets (Thrombocytes) CRP (C-Reactive Protein) MCV (Mean Corpuscular Volume)
€199,-

Medical reviewer

Medical standards

Dr. Naimi oversees the medical standards behind our content and assessments.

Medical policy
CIBG Ministerie van Volksgezondheid,
Welzijn en Sport Official BIG registration BIG 49928676701 Opens in a new tab

Vitamin D (25-OH)

€35,-