25 hydroxyvitamin D is a common fat-soluble vitamin that regulates the metabolism of calcium and phosphorus in the body. 25 hydroxyvitamin D is derived from the hydroxylation of vitamin D in the body through the liver and is a very direct indicator of vitamin D stores in the body. The level of 25 hydroxyvitamin D in the body has a clear clinical significance for the diagnosis of diseases such as rickets, postmenopausal osteoporosis, osteochondrosis, renal bone disease or non-bone related diseases, which require vitamin D supplementation, and the effect of supplementation can be evaluated by checking 25 hydroxyvitamin D in the body. It can be used to diagnose whether a patient has vitamin D deficiency or vitamin D overdose and to guide clinical use and treatment.