The vitamin D blood test measures the level of vitamin D in your blood, most often in the form called 25-hydroxyvitamin D (also written 25(OH)D), which your body makes from vitamin D. According to MedlinePlus, measuring 25(OH)D is considered the most accurate way to see how much vitamin D is in your body. The test may also be labeled 25(OH)D, calcidiol, cholecalciferol, ergocalciferol, vitamin D2, or vitamin D3.
A clinician may order this test to check whether you have too much or too little vitamin D, often when a bone problem or symptoms such as bone pain or muscle weakness could be related to a low level. Per MedlinePlus, it may also be considered for people at higher risk of low levels, including those with limited sun exposure, older adults, people with obesity, breastfed infants, and people with conditions affecting how the intestines absorb nutrients or how the liver and kidneys work. Your clinician decides if and when the test is appropriate for you.
Results are usually reported in nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L). MedlinePlus notes that many experts recommend a level of about 20 to 40 ng/mL (60 to 100 nmol/L), while others recommend about 30 to 50 ng/mL (75 to 125 nmol/L). These figures are general reference points only. As MedlinePlus states, "Normal value ranges may vary slightly among different laboratories," and they can also differ by age, sex, and the testing method used. The reference range printed on your own lab report is what applies to your result, and a number by itself is not a diagnosis.
A higher-than-normal level (sometimes called hypervitaminosis D) is, per MedlinePlus, most commonly associated with getting too much vitamin D from supplements. Very high levels can be linked to too much calcium in the blood (hypercalcemia) and may be associated with kidney damage or strain on other organs. These are general possibilities, not a diagnosis or a complete list of causes.
A lower-than-normal level may be associated with vitamin D deficiency. MedlinePlus notes this can be seen with limited sun exposure, not getting enough vitamin D in the diet, difficulty absorbing vitamin D from food, certain liver or kidney conditions that affect how the body converts vitamin D, or the use of some medications. These are general associations that may suggest a cause, not a diagnosis or a full list. A vitamin D result is interpreted by your clinician alongside your symptoms, history, other test results, and overall health. This is general information, not medical advice.
Reference ranges vary by laboratory, age, sex, and method — the range on your own report is what applies to you. A single value out of range doesn’t confirm any condition; your clinician interprets it alongside your symptoms, history, and other results. This page is general information, not medical advice.
General reference, not medical advice, and not a substitute for your clinician. Lab reference ranges and interpretation depend on the laboratory and on your individual situation — discuss your results with a licensed healthcare professional.