Low serum total IgE is not specific to a particular disease, but is commonly seen in tumor patients, after application of chemotherapy drugs, long-term use of immunosuppressants or gammaglobulinemia. The normal range of serum total IgE in normal adults is 20-200 IU/mL. IgE represents the total amount of immunoglobulin in the blood, and the human body has a low level of it. This indicator is more sensitive to the detection of allergens and inflammatory reactions, and usually rises if there is an allergic reaction, an infection, or an immune system disease. Decrease of this indicator is common in immunocompromised patients, tumors, after application of chemotherapeutic drugs, long-term use of immunosuppressive drugs and gammaglobulinemia. As the test index is affected by the environment, specimen, the operation of the test personnel and other factors, if the test index is only slightly low, it can be regularly rechecked, such as a significant decrease in the recommendation to consult a doctor to clarify the cause of the disease, so as to avoid delay in the condition.