The short answerA vitamin D blood test measures 25-hydroxyvitamin D, or 25(OH)D, the form your liver makes and the most accurate gauge of how much vitamin D your body has. By NIH’s cutoffs, 20 ng/mL or higher is adequate for most healthy people and below 12 ng/mL puts you at risk of deficiency, while the Endocrine Society’s 2011 guideline called below 20 ng/mL deficient and 21 to 29 ng/mL insufficient (its 2024 guideline names no cutoffs). Routine testing isn’t recommended for healthy adults, so ask your physician whether you need one.
Maybe a vitamin D blood test showed up on your lab order, or your result came back flagged and you’re not sure what it means. This guide explains what the test measures, who needs it, how to prepare, and how to read your number, including a vitamin D levels chart that puts the NIH and Endocrine Society cutoffs side by side. For the signs and causes of low vitamin D, see our guide to vitamin D deficiency in Florida.
What does a vitamin D blood test measure?
Vitamin D from sunlight, food, and supplements isn’t active when it enters your body. Your liver first converts it to 25-hydroxyvitamin D, also called calcidiol, and your kidneys then turn some of that into the active hormone, 1,25-dihydroxyvitamin D, or calcitriol. The standard vitamin D blood test measures the first form, 25(OH)D, because it reflects both the vitamin D your skin makes and what you get from food and supplements.
There’s a practical reason too. NIH notes that 25(OH)D stays in the blood a fairly long time, with a half-life of about 15 days, while the active form lasts only hours and is tightly controlled by parathyroid hormone, calcium, and phosphate. The active form usually doesn’t drop until a deficiency is severe, so it’s a poor gauge of your vitamin D supply.
Other names for the 25-hydroxy vitamin D test
Your lab order may call it a 25-hydroxyvitamin D test, 25-OH vitamin D, 25(OH)D, a calcidiol test, a 25-hydroxycholecalciferol test, or a vitamin D2 or D3 test. MedlinePlus lists all of these names for the same blood test.
25-hydroxy vs. 1,25-dihydroxy vitamin D test
The 1,25-dihydroxyvitamin D test, sometimes called active vitamin D, is a different test. MedlinePlus explains that it isn’t usually used to check whether you have enough vitamin D, but it may be used to monitor kidney problems or to find the cause of abnormal calcium levels. The Endocrine Society’s 2011 guideline also recommended against using it to judge vitamin D status, reserving it for monitoring certain disorders of vitamin D and phosphate metabolism.
Who should get a vitamin D blood test?
Not everyone. MedlinePlus says routine vitamin D testing isn’t recommended for everyone, and two expert groups have looked closely at testing healthy adults. The U.S. Preventive Services Task Force found the evidence insufficient to weigh the benefits and harms of screening adults without symptoms. The Endocrine Society’s 2024 guideline suggests against routine 25(OH)D testing in healthy people, including those with obesity or a darker complexion and during pregnancy.
Testing makes sense when there’s a medical reason. MedlinePlus lists these common ones:
- A condition linked to low vitamin D, such as osteomalacia, low bone density, osteopenia, or osteoporosis
- Symptoms such as bone pain, muscle weakness or aches, soft bones, or fractures
- Weight-loss surgery, or a condition that limits nutrient absorption, such as Crohn’s disease, ulcerative colitis, or celiac disease
- Kidney or liver disease that affects how your body converts vitamin D
- Medicines that affect vitamin D levels, including certain statins, steroids, and weight-loss medicines
- Rarely getting sun on your skin, or not eating enough
- Checking whether treatment for a diagnosed deficiency is working, or symptoms that suggest too much vitamin D
Guidance has shifted over time. The Endocrine Society’s 2011 guideline recommended screening people at risk, a list that included people with obesity, pregnant and breastfeeding women, and Black and Hispanic children and adults. Its 2024 guideline, which replaced the 2011 version, reversed course for several of those groups because the panel found no clinical trial evidence that routine screening helps.
How to prepare for a vitamin D blood test
Usually there’s nothing special to do. MedlinePlus notes that you typically don’t need to fast, though it depends on the lab and the testing method, so follow any instructions you’re given. Tell whoever orders the test about all the medicines, vitamins, and supplements you take, because they can affect your result, but don’t stop any medicine unless your provider tells you to.
The test itself is a standard blood draw from a vein in your arm and usually takes less than five minutes. You may feel a brief sting, and a small bruise or some throbbing afterward soon fades.
Vitamin D levels chart: NIH vs. the Endocrine Society
Results come in nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L), and 1 ng/mL equals 2.5 nmol/L. The same number can be read differently depending on which standard your lab or physician follows. NIH’s cutoffs come from the Food and Nutrition Board of the National Academies; the Endocrine Society’s are from its 2011 guideline.
How NIH and the Endocrine Society (2011) read it| 25(OH)D level | NIH | Endocrine Society (2011) |
|---|
| Below 12 ng/mL (below 30 nmol/L) | At risk of deficiency, which can lead to rickets in children and osteomalacia in adults | Deficient |
|---|
| 12 to under 20 ng/mL (30 to under 50 nmol/L) | Generally inadequate for bone and overall health | Deficient |
|---|
| 20 to 29 ng/mL (50 to 72.5 nmol/L) | Generally adequate for bone and overall health in healthy people | Insufficient, a range it defined as 21 to 29 ng/mL |
|---|
| 30 to 50 ng/mL (75 to 125 nmol/L) | Adequate | Its 2011 treatment goal was a level consistently above 30 ng/mL (75 nmol/L) |
|---|
| Above 50 ng/mL (above 125 nmol/L) | NIH: linked to potential adverse effects, particularly above 60 ng/mL (150 nmol/L) |
|---|
| Typically above 150 ng/mL (above 375 nmol/L) | NIH: the range typically seen in vitamin D toxicity, along with high blood calcium |
|---|
Two more reference points complete the picture. The Endocrine Society’s 2024 guideline, which replaced the 2011 one, does not name any 25(OH)D levels for sufficiency, insufficiency, or deficiency, and its panel found no clear evidence defining the best target level for preventing disease. And MedlinePlus notes that many experts recommend 30 to 80 ng/mL (75 to 200 nmol/L). Notice that part of that range sits above the 50 ng/mL level NIH links to potential adverse effects, one more sign that experts haven’t settled on a single target.
What is a normal vitamin D level?
It depends on who you ask, which is why “normal” on one report can be “low” on another. By NIH’s cutoffs, 20 ng/mL (50 nmol/L) or higher is adequate for bone and overall health in most healthy people. Many experts recommend 30 to 80 ng/mL instead, and the Endocrine Society’s 2011 guideline aimed for above 30 ng/mL. NIH also notes that optimal levels likely vary by stage of life, by race and ethnicity, and with the health measure being studied, and the U.S. Preventive Services Task Force states that no single blood level defines deficiency.
Vitamin D insufficiency vs. deficiency
Lab reports often sort results into deficient, insufficient, sufficient (or optimal), and toxic. MedlinePlus describes deficiency as very low levels that are likely to affect your bones and general health, and insufficiency as low levels that may weaken your bones and affect your health even if you have no symptoms. The numbers behind those words vary:
- Endocrine Society, 2011: deficiency below 20 ng/mL (50 nmol/L), and insufficiency 21 to 29 ng/mL
- NIH: risk of deficiency below 12 ng/mL (30 nmol/L), and 12 to under 20 ng/mL generally considered inadequate
- Endocrine Society, 2024: no cutoffs for either
So a level of 25 ng/mL is adequate by NIH’s standard but insufficient by the 2011 guideline. Neither label is a diagnosis by itself. What matters is the number, your symptoms and risk factors, and what your physician recommends.
Why vitamin D results can vary between labs
If two labs give you different numbers, your vitamin D may not be the only thing that changed. NIH notes that labs use different methods to measure 25(OH)D, mainly antibody-based tests and chromatography, and that this variability means a result can read falsely low or falsely high depending on the method and the lab. An international Vitamin D Standardization Program works to make results more consistent. If your number jumps, ask your physician whether the change is real or a lab difference.
Your report may also list vitamin D2 and D3 separately. MedlinePlus explains that D3 is what your skin makes or what you absorb from animal foods or a D3 supplement, while D2 comes from plant-based fortified foods or a D2 supplement. The two work about the same in your body, and the total 25(OH)D is the number to look at.
What happens after a low or high result?
A low level may mean you aren’t getting enough from food and sun, have trouble absorbing vitamin D, have kidney or liver disease that affects how you convert it, or take a medicine that lowers it, MedlinePlus explains. To raise it, your provider may recommend vitamin D supplements, more vitamin D foods, or both, which MedlinePlus notes is usually safer than more sun. Your physician sets the dose and decides whether and when to recheck. For food sources and daily amounts, see how to raise a low vitamin D level.
A high level usually comes from taking too much in supplements, and you’ll need to stop them. NIH notes that toxicity typically comes with levels above 150 ng/mL and high blood calcium, which can cause nausea, vomiting, muscle weakness, changes in mood or thinking, pain, loss of appetite, dehydration, excessive thirst and urination, and kidney stones. Experts don’t believe sun exposure alone causes vitamin D toxicity, though NIH notes that frequent tanning bed use can push levels very high.
Does MeliOra offer vitamin D testing?
No. MeliOra Elite Wellness doesn’t offer vitamin D testing, and none of its wellness shots is a dedicated vitamin D treatment. If you think you need a vitamin D blood test, your primary care physician is the right place to start: they can decide whether you have a reason to test, order it, and follow up on the result.
What MeliOra does offer is physician-led care that comes to you. Dr. Melanie Espinet, a board-certified family physician, gives every wellness shot herself at your home or office anywhere in the Tampa Bay service area or at the Lutz office by appointment, with no travel fee. The menu is Revital B12, Immune Renew, Revita, Lean Ease Lipo-C, MD Boost, and NAD Boost, at $30 each or 4 for $80. If you’re a MeliOra patient, you’re welcome to bring recent lab results and questions to your visit. See wellness shots in Lutz, or, if tiredness sent you looking, read about B12 deficiency symptoms, another cause of fatigue that a blood test can check.
Frequently asked questions
What is a 25-hydroxy vitamin D test?
It’s the standard vitamin D blood test. It measures 25-hydroxyvitamin D, the form your liver makes from the vitamin D you get from sun, food, and supplements, and it’s the most accurate way to see whether you have enough. It may also be listed as 25(OH)D, 25-OH vitamin D, or a calcidiol test.
Do you need to fast for a vitamin D blood test?
Usually not. MedlinePlus notes that fasting depends on the lab and the testing method, so follow any instructions you’re given. Do tell your provider about all the medicines and supplements you take.
What vitamin D level is considered deficient?
Below 12 ng/mL (30 nmol/L) puts you at risk of deficiency by NIH’s cutoffs, while the Endocrine Society’s 2011 guideline defined deficiency as below 20 ng/mL (50 nmol/L). The Endocrine Society’s 2024 guideline sets no cutoff, so ask your physician which standard your result was judged by.
Is a vitamin D level of 25 ng/mL good?
It’s adequate by NIH’s standard but insufficient by the Endocrine Society’s 2011 guideline. NIH considers 20 ng/mL or higher adequate for most healthy people, while the 2011 guideline called 21 to 29 ng/mL insufficient and aimed for a level above 30. Your physician can tell you whether it matters for your health.
Is vitamin D insufficiency the same as deficiency?
No. Deficiency is the lower, more serious range, and insufficiency is low but not as low. Under the Endocrine Society’s 2011 guideline, deficiency was below 20 ng/mL and insufficiency 21 to 29 ng/mL, while NIH calls 12 to under 20 ng/mL inadequate and below 12 ng/mL a risk of deficiency.
What is the difference between 25-hydroxy and 1,25-dihydroxy vitamin D?
25-hydroxyvitamin D is the circulating form your liver makes, and it’s the test used to check whether you have enough vitamin D. 1,25-dihydroxyvitamin D is the active hormone made mainly in the kidneys; its level is tightly controlled and usually doesn’t fall until a deficiency is severe, so it’s used mainly for kidney, calcium, and other specific conditions.
How often should you check your vitamin D level?
Only as often as your physician has a reason to. The Endocrine Society’s 2024 guideline suggests against routine testing in healthy people, including routine follow-up tests to adjust a supplement dose. If you’re being treated for a diagnosed deficiency, your physician may recheck to see whether your level is improving.
Does MeliOra offer vitamin D testing?
No. MeliOra doesn’t offer vitamin D testing, and none of its wellness shots is a dedicated vitamin D treatment. Your primary care physician can decide whether you need a vitamin D blood test and order it.
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