Immunoglobulin is mainly tested by drawing blood from a vein, and fasting is required for blood collection. Immunoglobulins are proteins with antibody activity in the human body, with antibacterial, antiviral and cellular immunity enhancement functions, they are important components of the body’s resistance to disease, and can be used to assist in the diagnosis of rheumatic diseases such as systemic lupus erythematosus, hematological disorders such as multiple myeloma, and infectious diseases such as viral hepatitis. Since diet can affect the accuracy of immunoglobulin, it is necessary to maintain an empty stomach during blood collection, usually after 8:00 p.m. on the previous day, and it is not recommended to eat too greasy or stimulating food before the test. It is recommended that women try to avoid the menstrual period for the test, so as not to affect the accuracy of the results. It is recommended to go to the laboratory of regular hospitals to improve the immune function measurement.