Vitamin D, 25-Oh, Total (25-Hydroxyvitamin D) Biomarker Testing
It measures your vitamin D status to guide bone, muscle, and immune health decisions, with convenient ordering and Quest lab access via Vitals Vault.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
Vitamin D is one of those nutrients that quietly affects a lot of day-to-day function. If your level is low, you might notice vague issues like fatigue, muscle aches, frequent illness, or slower recovery, but you also might feel completely fine.
A Vitamin D, 25-Oh, Total test (also called 25-hydroxyvitamin D or 25(OH)D) is the standard blood test used to estimate your overall vitamin D status. It helps you and your clinician decide whether your current sun exposure, diet, and supplements are enough—and whether it makes sense to change your plan.
Because vitamin D levels can move with seasons, travel, and supplement dose changes, this is also a useful test to repeat after you make an adjustment. The goal is not to “chase a perfect number,” but to get into a range that supports bone and muscle health while avoiding excess.
Do I need a Vitamin D, 25-Oh, Total test?
You may want this test if you have risk factors for low vitamin D, even if you do not have obvious symptoms. Common reasons include limited sun exposure, darker skin pigmentation, living at higher latitudes, consistent sunscreen use, being older, or having obesity (vitamin D can be sequestered in fat tissue).
Testing is also reasonable if you have bone or muscle concerns, such as frequent fractures, low bone density, muscle weakness, or persistent aches. If you are managing conditions that affect absorption—such as celiac disease, inflammatory bowel disease, or a history of bariatric surgery—your clinician may use 25(OH)D to check whether you are absorbing enough.
If you already take vitamin D supplements, a blood test can prevent guesswork. It helps you see whether your dose is too low to be effective or high enough to push you toward an unsafe range.
Your result is best used to support clinician-directed care and follow-up decisions. It cannot diagnose the cause of a low level on its own, but it can point to the next most useful questions and companion labs.
This blood test is performed in a CLIA-certified laboratory; results should be interpreted with your clinician and your full health context, not used as a standalone diagnosis.
Lab testing
Order Vitamin D, 25-Oh, Total and get a clear report you can share with your clinician.
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
Vitals Vault lets you order a Vitamin D, 25-Oh, Total test directly, so you can check your status without waiting for a separate office visit just to place the order. After your blood draw, you receive a clear lab report you can share with your clinician.
If you want help making sense of the number, PocketMD can walk you through what “low,” “in range,” and “high” typically mean, what factors can skew results, and what follow-up questions to bring to your next appointment.
This test is especially useful for trending. If you change your supplement dose, travel to a sunnier climate, or shift your diet, you can recheck in a clinician-appropriate timeframe to confirm the plan is working and to avoid overshooting.
- Order online and complete your draw through a national lab network
- PocketMD guidance to help you interpret results and plan next steps
- Easy retesting to track seasonal changes or dose adjustments
Key benefits of Vitamin D, 25-Oh, Total testing
- Shows your overall vitamin D status using the standard marker clinicians rely on (25-hydroxyvitamin D).
- Helps explain bone, muscle, and fatigue-related symptoms when the cause is not obvious.
- Supports safer supplement decisions by reducing under-dosing and avoiding excessive dosing.
- Guides follow-up timing after lifestyle changes, travel, or seasonal shifts in sun exposure.
- Adds context for bone-health planning when paired with calcium, parathyroid hormone (PTH), and alkaline phosphatase.
- Helps identify when malabsorption or medication effects may be contributing to low levels.
- Makes it easier to trend your level over time and discuss a targeted plan with PocketMD or your clinician.
What is Vitamin D, 25-Oh, Total?
Vitamin D, 25-Oh, Total measures the amount of 25-hydroxyvitamin D in your blood. This is the main circulating “storage” form of vitamin D and the best single lab marker for estimating your vitamin D status.
Vitamin D comes from two main sources: your skin makes it after UVB sun exposure, and you can also get it from food and supplements. Your liver converts vitamin D into 25-hydroxyvitamin D (25(OH)D). Your kidneys and other tissues then convert it into the active hormone form (1,25-dihydroxyvitamin D), which helps regulate calcium and phosphorus balance.
Because 25(OH)D has a longer half-life than the active form, it reflects your recent-to-medium-term vitamin D supply. That is why clinicians typically order 25(OH)D—not 1,25-dihydroxyvitamin D—when they want to assess deficiency or monitor supplementation.
What vitamin D does in your body
Vitamin D supports calcium absorption and bone mineralization, which is why low levels are linked with osteomalacia in adults and rickets in children. It also plays roles in muscle function and immune signaling. These effects are real, but they are not always specific, so testing helps separate vitamin D issues from other common causes of similar symptoms.
Why “total” matters
“Total” 25(OH)D generally reflects the combined contribution of vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). If you take prescription D2 or over-the-counter D3, the total result is meant to capture your overall status regardless of the source.
What do my Vitamin D, 25-Oh, Total results mean?
Low Vitamin D (25-Oh, Total)
A low result usually means your body’s vitamin D supply is not keeping up with your needs. This can happen from limited sun exposure, low dietary intake, higher body fat, or reduced absorption from the gut. If your level is low and you also have abnormal calcium, elevated PTH, or bone symptoms, your clinician may look for secondary hyperparathyroidism or other bone-mineral issues. Low vitamin D is common, and the next step is often a practical plan plus a repeat test to confirm improvement.
In-range (often considered “sufficient”) Vitamin D
An in-range result suggests your current mix of sun exposure, diet, and supplements is meeting your body’s baseline needs. If you still have symptoms, it is a sign to look beyond vitamin D rather than escalating doses automatically. Many people benefit from trending across seasons, because a “good” summer level can drift down in winter. Your clinician may also interpret your result differently if you have osteoporosis, chronic kidney disease, or other conditions that change vitamin D needs.
High Vitamin D (25-Oh, Total)
A high result most often reflects supplement intake that is higher than your body requires. Very high levels can raise the risk of high calcium (hypercalcemia), which can cause nausea, constipation, confusion, increased thirst, or kidney stones. If your vitamin D is high, clinicians commonly review your supplement dose and also check calcium and kidney function to ensure safety. Do not stop prescribed therapy without guidance, but do treat a high result as a prompt to reassess dosing.
Factors that influence Vitamin D results
Season and geography matter: levels often peak after summer and drop after winter, especially at higher latitudes. Body size can influence results because vitamin D is fat-soluble and may distribute into fat tissue. Absorption issues (celiac disease, inflammatory bowel disease, bariatric surgery) and certain medications can lower levels, while high-dose supplements can raise them quickly. Lab reference ranges and units can vary, so compare your number to the reference interval on your report and interpret it alongside calcium, PTH, and your clinical picture.
What’s included
Frequently Asked Questions
What is the difference between Vitamin D and Vitamin D, 25-Oh, Total?
“Vitamin D, 25-Oh, Total” is the blood test that measures 25-hydroxyvitamin D (25(OH)D), the main circulating form used to assess vitamin D status. When people say “vitamin D level,” they usually mean this test. Other vitamin D-related tests exist, but they are used for specific medical situations and do not replace 25(OH)D for routine status checks.
Do I need to fast for a Vitamin D blood test?
Fasting is usually not required for a Vitamin D, 25-Oh, Total test. If your clinician or your order includes other labs that do require fasting (such as a lipid panel), follow the instructions for the full set of tests you are getting that day.
What is a good Vitamin D level?
A “good” level depends on the reference range used by your lab and your personal health context. Many clinicians consider a mid-range, sufficient result appropriate for general bone and muscle health, while people with osteoporosis, malabsorption, or other conditions may have different targets. Use the reference interval on your report and review it with your clinician rather than relying on a single universal cutoff.
How long after starting supplements should I retest Vitamin D?
A common approach is to retest after enough time has passed for your level to stabilize following a dose change. The right timing depends on your starting level, your dose, and whether you are correcting a deficiency under medical supervision. If you are using high-dose therapy or have symptoms, your clinician may recommend earlier follow-up and may pair retesting with calcium and PTH.
Can Vitamin D be high from sunlight alone?
It is uncommon for sunlight alone to push 25(OH)D into a very high range. High results are more often related to supplements, especially high-dose daily products or stacking multiple supplements that each contain vitamin D. If your result is high, review all sources, including multivitamins and combination products.
Why would my Vitamin D be low even if I take supplements?
Low levels despite supplementation can happen if the dose is too low for your needs, if you are not taking it consistently, or if absorption is reduced. Taking vitamin D with a meal that contains fat can improve absorption for some people. Conditions that affect the gut, certain medications, and higher body weight can also make it harder to raise levels.
Should I test 1,25-dihydroxyvitamin D instead of 25-hydroxyvitamin D?
For most people, no. 25-hydroxyvitamin D (the 25-Oh, Total test) is the standard way to assess vitamin D status. The active form, 1,25-dihydroxyvitamin D, is tightly regulated and can be normal or even high when your overall stores are low, so it is typically reserved for specific kidney, parathyroid, or rare metabolic questions.