A Vitamin D test is a blood test used to measure the level of vitamin D in the body. Vitamin D is essential for bone health, calcium absorption, immune function, and overall well-being. The test helps diagnose vitamin D deficiency, monitor treatment, or evaluate conditions related to abnormal calcium levels. There are two main forms of vitamin D measured in the test: 1. 25-Hydroxyvitamin D [25(OH)D]: This is the most common and accurate marker for assessing vitamin D status. It reflects the total amount of vitamin D from sunlight exposure, food intake, and supplements. 2. 1,25-Dihydroxyvitamin D [1,25(OH)2D]**: This active form of vitamin D is sometimes measured in specific cases, such as kidney disease or rare metabolic disorders, but it is not typically used for general deficiency screening. Vitamin D testing is recommended for individuals at risk of deficiency, including those with limited sun exposure, darker skin, older adults, or conditions affecting vitamin D absorption. Results guide healthcare providers in determining whether dietary changes, supplements, or other interventions are necessary to restore optimal vitamin D levels and promote better health outcomes.