Vitamins are trace organic substances that are essential for biological growth and metabolism. They are divided into two categories: fat-soluble vitamins and water-soluble vitamins. The former includes vitamin A, vitamin D, vitamin E, vitamin K, etc. The latter includes B vitamins and vitamin C. In humans and animals, vitamin deficiency does not allow normal growth and specific lesions occur, which is known as vitamin deficiency. Checking vitamin D, vitamin B12, and serum folate can be used for clinical diagnosis of various nutritional deficiencies Vitamin D is a fat-soluble steroid with the basic chemical structure of cholesterol. The main forms are vitamin D2 (calcitriol) and vitamin D3 (cholecalciferol). Vitamin D3 is produced in the skin after exposure to sunlight or ultraviolet B rays from artificial light sources. The function of vitamin D is to maintain normal blood calcium and phosphorus concentrations to increase calcium absorption in the small intestine, to support the mineralization of bone-like substances and other vitamins, hormones and minerals, and is important for the formation and maintenance of strong bones. Vitamin B12 is the only vitamin that requires intestinal secretions (endogenous factors) in order to be absorbed. Some people lack this endogenous factor due to gastrointestinal abnormalities and can suffer from pernicious anemia even with adequate dietary sources. The role of vitamin B12: 1, promote the development and maturation of red blood cells, so that the body’s hematopoietic function in a normal state, to prevent pernicious anemia; 2, in the form of coenzyme, can increase the utilization of folic acid, promote the metabolism of carbohydrates, fats and proteins; 3, with the role of activation of amino acids and promote the biosynthesis of nucleic acids, can promote the synthesis of proteins, it has an important role in the growth and development of infants and children 4, eliminate irritability, concentration, enhance memory and balance, is an indispensable vitamin for the sound function of the nervous system. Folic acid is a water-soluble B vitamin. The important nutritional role of folic acid in the human body was confirmed as early as 1948. Deficiency of folic acid in humans (or other animals) can cause megaloblastic anemia and emotional changes caused by folic acid deficiency, which can disappear with folic acid supplementation. Folic acid deficiency in pregnant women increases the incidence of pre-eclampsia and placental abruption, and megaloblastic anemia predisposes pregnant women to intrauterine growth retardation, preterm delivery and low birth weight of the newborn. Deficiency of folic acid in early pregnancy also predisposes the fetus to neural tube abnormalities (e.g. spina bifida, anencephaly, etc.). Folic acid deficiency can cause hyperhomocysteinemia, which increases the risk of cardiovascular disease. Patients with folic acid deficiency can be considered when serum folate test values are below normal reference values. Serum folate level is an early indicator of the body’s folate status; the folate content in red blood cells is a more realistic indicator of the body’s folate stores than the serum folate content; therefore, the folate content in red blood cells is the most reliable indicator of the body’s folate stores. The combination of vitamin B12, serum folate, and serum ferritin into a triple test for anemia is mainly for the convenience of clinicians and patients, so that physicians can understand the cause of anemia in patients. Patients with serum ferritin test values below normal reference values can be considered to have iron deficiency anemia, and if they are above normal reference values, the following diseases can be considered: chronic liver disease, long-term renal dialysis suffering from proliferative anemia diagnosis.