The Serum 25 Hydroxyvitamin D test is an important indicator of the amount of vitamin D in the body to assess calcium absorption. Serum 25 hydroxyvitamin D is the active form of vitamin D in the body, and the body needs to synthesize 25 hydroxyvitamin D after vitamin D intake in order to function and promote calcium absorption. Vitamin D deficiency can lead to rickets in young children, with clinical manifestations of irritability, excessive sweating, lethargy, loss of appetite, occipital baldness, square skull, chicken chest, beaded chest, etc., and in severe cases, internal and external deformity of the knee joints can also occur, and osteochondrosis can occur in adults, with clinical manifestations of weakness, generalized pain and difficulty in walking, and the monitoring of serum 25 hydroxyvitamin D can serve as a reference to supplement the vitamin D.