The Vitamin D Total Test measures the overall level of vitamin D in your blood, including both 25-hydroxyvitamin D2 and D3 forms. Vitamin D is essential for maintaining healthy bones, supporting the immune system, and regulating calcium and phosphorus levels in the body. This test helps detect vitamin D deficiency, insufficiency, or excess, which can lead to conditions like osteoporosis, bone pain, muscle weakness, or other health issues.