Hydroxyvitamin D is the main form of vitamin D in the body, known as 25-hydroxyvitamin D. It is mainly found in the liver and is used as a clinical indicator to determine the presence or absence of vitamin D. It can be used as an important indicator for the early determination of rickets, and also as an important indicator for osteoporosis and osteochondrosis, and many children with rickets need vitamin D supplementation in clinical practice. The 25-hydroxyvitamin D level needs to be closely checked to develop an oral dose to prevent triggering excessive vitamin D intake, which can lead to vitamin D toxicity, and also to assess, the outcome of treatment according to the 25-hydroxyvitamin D response level. If the test response 25-hydroxyvitamin D is too high, it indicates excessive vitamin D intake, and if 25-hydroxyvitamin D is low, it indicates vitamin D deficiency, excessive loss, impaired absorption, rickets, osteomalacia, and also seen in patients with malignancy, cardiovascular disease, and diabetes.