Eosinophils are a type of leukocyte and are called eosinophils because the cytoplasm contains particles that bind to acids. Normally, eosinophils make up 0.5%-5% of the leukocytes in the peripheral blood, and less than 0.5% is a decrease in the proportion of eosinophils. Clinically, decreased eosinophils can be seen in infectious diseases, such as typhoid and paratyphoid infections, which may result in decreased eosinophils. In addition, when the human body is in a state of stress, such as burns, trauma, major surgery, etc., there will also be a mild decrease in the proportion of eosinophils. In addition, long-term glucocorticoid patients, such as immune thrombocytopenia patients, long-term oral glucocorticoid, will also appear to reduce the proportion of eosinophils. Therefore, decreased eosinophil ratio can be seen in a variety of diseases.