Vitamin D (25-Hydroxy)
Measures vitamin D levels in the body to assess bone health, immune function, and overall vitamin D status
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Lab testing services linked from this site are not available to residents of Alaska, Arizona, or Hawaii, unless otherwise noted on the lab's own website.
This publication is not intended to solicit the purchase of laboratory testing from any individual consumer.
What this test measures
This test measures 25-hydroxyvitamin D, the form of vitamin D that circulates most abundantly in the bloodstream and serves as the most reliable gauge of overall vitamin D status. The body obtains vitamin D through two pathways: the skin synthesizes vitamin D3 (cholecalciferol) when exposed to sunlight, while dietary sources and supplements provide both vitamin D3 (from animal-based foods) and vitamin D2 (ergocalciferol, from fortified plant-based foods). Both forms function similarly once converted to 25-hydroxyvitamin D in the liver.
Vitamin D plays a central role in calcium and phosphorus absorption, which makes it indispensable for building and maintaining strong bones. When vitamin D levels remain low over time, calcium absorption in the gut drops, which can trigger a cascade: the parathyroid glands compensate by releasing more parathyroid hormone, accelerating bone turnover and potentially weakening the skeleton. Beyond bone health, vitamin D supports immune system regulation, muscle function, and nervous system signaling. This test helps identify deficiency or excess so that corrective steps can be taken before complications develop.
Who should consider this test
You might consider this test if you are experiencing any of the following:
- Individuals over the age of 65, as both skin production of vitamin D and gut absorption become lower with aging
- Those who are obese, have had weight-loss surgery, or have conditions that affect nutrient absorption like celiac disease, Crohn disease, or ulcerative colitis
- People who spend most of their time indoors, have darker skin pigmentation, or live in northern latitudes with limited sun exposure
- Individuals experiencing bone pain, muscle weakness, muscle aches, fatigue, or mood changes like depression
- Those with a personal or family history of rickets, osteoporosis, or bone fractures
- People with chronic kidney disease, liver disease, or taking certain medications that may affect vitamin D metabolism
What to expect
Preparation
Usually, fasting is not required for this test, but this may depend on the laboratory and testing method used. Individuals should follow any specific instructions provided by the testing facility regarding eating before the test.
Sample Type
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or syringe.
Collection
A trained phlebotomist will collect the blood sample at the laboratory. The procedure typically takes just a few minutes and involves minimal discomfort. No doctor visit required for this simple lab test.
Turnaround
Results are typically available within 1-3 business days after the sample is received at the laboratory.
Understanding your results
Results are reported in nanograms per milliliter (ng/mL). Most expert guidelines place the optimal range somewhere between 20 and 50 ng/mL, though specific cutoffs vary depending on the organization issuing the recommendation. Many people with low vitamin D levels experience no obvious symptoms at all, while others may notice vague complaints like fatigue or muscle discomfort that overlap with numerous other conditions. Healthcare providers use these results alongside clinical context to determine whether supplementation, dietary changes, or increased sun exposure may be appropriate.
| Population | Reference Range | Notes |
|---|---|---|
| Adults | 30-100 ng/mL | Many experts recommend maintaining vitamin D levels between 30-50 ng/mL for optimal health benefits |
| Deficiency | Less than 20 ng/mL | Vitamin D deficiency is defined as serum 25-hydroxy vitamin D levels below 20 ng/mL |
| Insufficiency | 21-29 ng/mL | Vitamin D insufficiency is defined as levels between 21 and 29 ng/mL |
Reference ranges shown are general guidelines. Your lab report will include the specific reference range used by the laboratory that processed your sample, which is the authoritative range for interpreting your results.
What does a “Low” result mean?
Low vitamin D levels can lead to serious health conditions. In adults, severe vitamin D deficiency may cause osteomalacia, which results in weak bones, bone pain, and muscle weakness. Low levels can cause muscle weakness and cramps, fatigue, and depression, and may lead the body to take calcium from bones, resulting in accelerated bone demineralization and potentially osteomalacia in adults. Even mild, chronic vitamin D deficiency can lead to chronic hypocalcemia and secondary hyperparathyroidism, increasing the risk of osteoporosis, falls, and fractures, particularly in older individuals.
What does a “High” result mean?
Higher-than-normal vitamin D levels (hypervitaminosis D) are most commonly caused by taking excessive vitamin D supplements. This can result in too much calcium in the blood (hypercalcemia), which may lead to symptoms and kidney damage. Vitamin D intoxication typically does not occur until blood levels are above 150-200 ng/mL and is associated with hypercalcemia, hypercalciuria, and often hyperphosphatemia. Symptoms of vitamin D toxicity may include increased thirst and urination, poor appetite, constipation, and other complications.
Privacy & confidentiality
All test orders are authorized and results reviewed by an independent, board-certified physician who is not the patient's personal doctor. Your vitamin D test results are completely confidential and handled with the highest level of privacy protection. Results are <u>not reported to your personal doctor</u> unless you specifically choose to share them. The test results are <u>not part of your medical records</u> and will <u>not appear on insurance statements</u> or explanation of benefits (EOB) forms. We understand that some individuals prefer to monitor their vitamin D levels privately, whether due to concerns about insurance implications or simply personal preference. Your test results belong to you alone. We do not share your information with employers, insurance companies, or government agencies. All testing is conducted through certified laboratories that follow strict confidentiality protocols, ensuring your health information remains secure and private. This confidential testing approach allows individuals to proactively monitor their vitamin D status and take appropriate steps to optimize their health without concerns about privacy or medical record documentation.
Frequently asked questions
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Read ArticleLast reviewed: April 10, 2026
CPT Code: 82306
This test may not be available in: NY, NJ, RI
This page is for informational purposes only and does not constitute medical advice. Always consult with a healthcare provider regarding any health concerns. LevelPanel does not diagnose, treat, or prescribe.
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LevelPanel has no business or affiliate relationship with Quest or LabCorp. These links are provided as a public service.
Lab testing services linked from this site are not available to residents of Alaska, Arizona, or Hawaii, unless otherwise noted on the lab's own website.
This publication is not intended to solicit the purchase of laboratory testing from any individual consumer.
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