Vitamin D test
You produce vitamin D in your skin under sunlight. At Dutch latitude the sun sits too low between roughly October and April to manage that. What you are left with is your store and what you eat or supplement.
The value measured is 25-OH vitamin D, also called calcidiol. That is the storage form and the best measure of your status over recent weeks. There is an active form, 1,25-OH, but it says little about your store and is not normally measured.
Vitamin D plays a role in calcium absorption, bone building and immune function. A low value often causes no symptoms at all, which is precisely why measuring is the only way to know.
Vitamin D on its own?
Message whether you want it alone or alongside B12 and ferritin. The latter is often more sensible, because those three tend to belong to the same story when you feel tired.
Book your blood test now. Reachable Monday to Saturday, 08:00 to 18:00.
When to measure this
- At the end of winter, around February or March, when your value is at its lowest.
- If you are outdoors little or work indoors during daylight.
- If you have darker skin. More pigment means more sun exposure for the same production.
- If you wear covering clothing.
- If you already supplement and want to know whether your dose is landing. Measure after 8 to 12 weeks.
- With persistent fatigue, alongside the markers on the fatigue page.
What is actually drawn
If you want to know whether more is going on, the Vitamins and Minerals package is the sensible choice. It adds B12, folate, full iron status, magnesium, zinc and calcium.
Preparation
No fasting required. If you supplement vitamin D, skip the dose on the morning of the draw for a cleaner picture of your underlying status. There is nothing else to prepare.
Which package includes this
Measuring this marker on its own is possible too. A single assay is possible from € 149, with the draw at your home within the A10 ring included. Outside it the price is on request. For reference, providers with a collection point typically charge 59 to 69 euro for a single marker, and you travel there yourself.
* All prices apply to a blood draw at your home within the A10 ring. One fixed price, everything included: a BIG-registered nurse who draws your blood at home, the materials, the analysis by a recognised laboratory and a report you understand. Live outside it? Then the price is on request: WhatsApp your postcode and what you want tested.
What your result means
The laboratory provides a reference range. Alongside it you get the stricter target range used in preventive practice. Those two do not sit in the same place, and that gap is where it gets interesting: you can be above the lab floor and still be at the low end of what is desirable.
A low value does not demonstrate a condition. It suggests supplementation may be worthwhile, and gives you a reason to measure again in a few months to see whether it worked.
On the difference between a lab reference and a target range, see this article. If you feel unwell while your value sits inside the reference, read this one.
Frequently asked questions
When is the best time to measure vitamin D?
At the end of winter, around February or March.
That is the low point of the year. Measuring in August captures your best moment and tells you nothing about January.
Do I need to fast?
No.
You can eat normally. Skip your supplement that morning so you measure your underlying status rather than the peak from your capsule.
How long before supplementation shows up in blood?
Allow 8 to 12 weeks.
Vitamin D builds up slowly in fat tissue. Measuring sooner usually shows little difference.
Will my GP not just order this?
Only if there is a medical reason.
Without symptoms or risk factors it is usually not in the ordered panel. You can measure it yourself.
Can I have vitamin D drawn on its own?
Yes.
That is possible from € 149, with the draw at your home within the A10 ring included. The Vitamins and Minerals package is often more practical, because B12 and ferritin belong to the same set of complaints.
Note: a blood test gives you insight and direction. It does not prove or rule out a condition on its own. Results are meant for prevention and for tracking change over time, not as a diagnosis. For symptoms or values outside the reference range, see your GP.