2022/11/02 · In your bloodstream, Vitamin D2 and Vitamin D3 are changed into a form of Vitamin D called 25 hydroxyvitamin D, also known as 25 (OH)D. A Vitamin D blood test measures the level of 25 (OH)D in your blood. Abnormal levels of Vitamin D can indicate bone disorders, nutrition problems, organ damage, or other medical conditions.