The vitamin D test worth ordering is 25-hydroxyvitamin D. What we see readers get wrong most often is ordering this test when nothing about the result would change what they do.
The Verdict
The Two Vitamin D Tests and Which One You Want
Vitamin D exists in your blood in two forms that laboratories measure separately. Sunlight and food produce vitamin D, your liver converts it into 25-hydroxyvitamin D, and your kidneys convert a fraction of that into 1,25-dihydroxyvitamin D, the hormone that actually does the work.
| Test | What it is | When to order it |
|---|---|---|
| 25-hydroxyvitamin D | The storage form, with a half-life measured in weeks | This is the vitamin D status test. Order this one. |
| 1,25-dihydroxyvitamin D | The active hormone, with a half-life measured in hours | Tightly regulated, so it can read normal or high while stores are empty. Reserved for high calcium, kidney disease and sarcoidosis. |
Ordering the active form to assess status is the single most common mistake on a vitamin D requisition. Your body defends the active hormone level tightly, raising parathyroid hormone to keep it steady as stores fall. Someone genuinely depleted can therefore produce a normal or even raised 1,25-dihydroxyvitamin D result, which reads as reassurance while the storage form tells the opposite story.
What Counts as a Normal Vitamin D Level
The disagreement between the two published standards is real, and it sits precisely where most results land. The National Academies concluded in its dietary reference intake review that 20 ng/mL meets the needs of nearly everyone for bone health. The Endocrine Society used 30 ng/mL as sufficiency in its earlier clinical guidance.
| Result | How it is classified | What sits behind the number |
|---|---|---|
| Below 12 ng/mL (30 nmol/L) | Deficient by every standard | The range associated with rickets and osteomalacia. Both bodies agree here. |
| 12 to 20 ng/mL (30 to 50 nmol/L) | Inadequate for some | The National Academies place the population requirement inside this band. |
| 20 to 30 ng/mL (50 to 75 nmol/L) | Where the disagreement sits | Sufficient for bone health by the National Academies. Below the 30 ng/mL figure the Endocrine Society used in its earlier guidance. |
| Above 30 ng/mL (75 nmol/L) | Sufficient by every standard | No added benefit is established above this. Toxicity concerns start far higher. |
Both figures are defensible, because they answer different questions. The National Academies asked what a population needs to avoid bone disease. The Endocrine Society asked what an individual patient with a reason to be tested should be brought to. Our guide to normal versus optimal ranges covers why that distinction produces two numbers for one marker.
Units are the other source of confusion. United States laboratories report ng/mL and most others report nmol/L, and the conversion is a factor of 2.5. A result of 30 ng/mL and one of 75 nmol/L are the same blood.
Who Should Have a Vitamin D Test
Guidance has moved against routine testing, and the reasoning is worth understanding rather than just following. The United States Preventive Services Task Force (USPSTF) examined screening for vitamin D deficiency in asymptomatic adults and concluded that the evidence is insufficient to weigh the benefits against the harms. The Endocrine Society's 2024 guideline went further and advised against routine 25-hydroxyvitamin D testing in healthy people. Its stated reason was that no threshold reliably guides treatment in that group.
| Situation | Test? | Why |
|---|---|---|
| Healthy adult, no symptoms, no risk factors | Not recommended | The USPSTF found the evidence insufficient to assess screening in asymptomatic adults, and the Endocrine Society advises against routine testing in healthy people. |
| Osteoporosis, fracture, or bone pain | Yes | The result changes how the bone condition is managed. |
| Malabsorption: coeliac disease, Crohn's, bariatric surgery | Yes | Fat-soluble vitamin absorption is directly affected, and the deficiency can be severe. |
| Chronic kidney disease | Yes, and often the active form too | Kidney conversion of the storage form to the active hormone is impaired. |
| Raised blood calcium | Yes, including 1,25-dihydroxyvitamin D | This is one of the few settings where the active form is the right test. |
| Already taking a supplement and feeling well | Usually not | A result inside the range does not change the plan, and a result below it usually leads to the supplement already being taken. |
The pattern across those rows is that testing earns its place when a result changes a decision. In a healthy adult with no risk factors, a low-normal result generally leads to a supplement that carries little risk either way. That is the same place they would have arrived without the blood draw.
What the Result Does Not Tell You
A 25-hydroxyvitamin D result describes your stores and nothing else. It does not predict whether supplementation will improve how you feel. VITAL, a trial of 25,871 adults published in the New England Journal of Medicine in 2019, found that vitamin D supplementation did not lower the rate of cancer or cardiovascular events. Low vitamin D travels with poor health for reasons that include less time outdoors and more body fat, which makes it a marker of circumstances as much as a cause of them.
The result also says nothing about your calcium handling on its own. Where a clinician is investigating bone disease, the vitamin D level is read alongside calcium, phosphate, parathyroid hormone and alkaline phosphatase, and our guide to alkaline phosphatase covers that last one.
Who Should Skip This Test
A healthy adult with no bone disease, no malabsorption, normal kidney function and no raised calcium can skip it. So can anyone already taking a moderate vitamin D supplement who feels well, because the result rarely changes what they do next. Our guide to when to take vitamin D covers the supplement question, which is where most people who reach for this test actually want to end up.
What would change that answer is a reason for the result to matter. A fracture, a diagnosis of osteoporosis, bariatric surgery, coeliac disease, chronic kidney disease or a raised calcium all move this from a curiosity to a test worth doing. If any of those apply to you, ask specifically for 25-hydroxyvitamin D by name at your next appointment.
Frequently Asked Questions
What is the vitamin D blood test called?
The test you want is 25-hydroxyvitamin D, often written as 25(OH)D and sometimes as calcidiol. It measures the storage form your body holds for weeks, which is what makes it a status test. A different test, 1,25-dihydroxyvitamin D, measures the active hormone and is not a status test at all. If a requisition offers both, the storage form is the one that answers the question almost everyone is asking. Ask for it by name on the requisition.
Which vitamin D blood test is best?
25-hydroxyvitamin D measured by liquid chromatography with tandem mass spectrometry is the most accurate option. Reference laboratories use it. Most routine results come from immunoassays instead, which are cheaper and vary more between platforms. The CDC runs a standardisation programme that laboratories can certify against, which narrows the spread. A difference of several ng/mL between two laboratories can therefore be the method rather than a change in you. Track your results at one laboratory where you can.
What is a normal vitamin D level?
That depends on which body you ask. The disagreement is genuine rather than a rounding difference. The National Academies of Sciences, Engineering, and Medicine concluded that 20 ng/mL (50 nmol/L) meets the requirements of nearly all people for bone health. The Endocrine Society used 30 ng/mL (75 nmol/L) as its sufficiency threshold in earlier guidance. Everyone agrees that below 12 ng/mL is deficient. If your result lands between 20 and 30, which standard your laboratory prints decides whether your report is flagged.
Should I get my vitamin D tested?
If you are healthy and have no risk factors, current guidance says no. The USPSTF concluded that the evidence is insufficient to weigh the benefits and harms of screening asymptomatic adults. The Endocrine Society advised against routine 25-hydroxyvitamin D testing in the general healthy population in its 2024 guideline. Testing is worthwhile where the result changes something: osteoporosis, malabsorption, chronic kidney disease, raised calcium, or a bone condition under active management.
How accurate is the vitamin D blood test?
Accuracy depends on the method, and the spread between methods is wider than most people expect. Immunoassays, which produce most routine results, can differ from mass spectrometry and from each other by several ng/mL on the same sample. That variation matters most for anyone whose result sits near a threshold, because a laboratory change can move a result across the line without anything changing in the person. Repeating at the same laboratory is the way to make a trend interpretable.
Is a vitamin D blood test covered by insurance?
Coverage follows the indication rather than the test. Where a documented condition justifies it, such as osteoporosis, malabsorption or chronic kidney disease, the test is generally covered. Screening in a healthy adult often is not, which follows directly from the USPSTF finding that the evidence does not support routine screening. Coverage rules differ between insurers and change, so the reliable move is to ask what diagnosis code is going on the requisition before the blood is drawn.
How long does a vitamin D blood test take?
The draw is a single tube and takes a minute. Results typically come back within a few working days, because 25-hydroxyvitamin D is usually batched rather than run individually, and mass spectrometry runs less often than immunoassay. Nothing about the test is urgent in a healthy adult, since the storage form moves over weeks and a few days makes no difference to what the result means.
Do I need to fast for a vitamin D blood test?
No. 25-hydroxyvitamin D is not affected by a recent meal, so fasting is unnecessary for this test on its own. Any fasting instruction you are given comes from something else drawn at the same visit, such as a lipid or metabolic panel. Season matters more than the meal: levels fall through winter at higher latitudes, so a result taken in February and one taken in August are not directly comparable.