The Vitamin D blood test measures the levels of 25-hydroxyvitamin D (25(OH)D) in the bloodstream. Vitamin D is a fat-soluble vitamin that is important for bone health, immune function, and other physiological processes in the body. The body can produce vitamin D when the skin is exposed to sunlight, and it can also be obtained from certain foods and supplements.

The Vitamin D blood test is used to assess vitamin D status and detect deficiencies. The normal range for 25(OH)D levels in the blood is between 30 and 100 ng/mL. Levels below 20 ng/mL are considered deficient, while levels between 20 and 30 ng/mL are considered insufficient.

Vitamin D deficiency is relatively common, especially in certain populations, such as older adults, people with dark skin, and those who live in areas with limited sunlight exposure. Symptoms of vitamin D deficiency may include bone pain, muscle weakness, fatigue, and an increased risk of fractures. Vitamin D deficiency has also been linked to an increased risk of several chronic diseases, such as osteoporosis, diabetes, and certain cancers.

The Vitamin D blood test can be used to diagnose and monitor vitamin D deficiency and to guide treatment with vitamin D supplements. Vitamin D supplements are available in various forms, including vitamin D2 and vitamin D3. Vitamin D3 is the more potent and stable form and is generally preferred for supplementation.