AIDS is an infectious disease that occurs when the human immunodeficiency virus (HIV) invades the human body. Because HIV infection replicates in large numbers in the human body, it selectively destroys CD4+ T lymphocytes, causing a decrease in the number of peripheral blood leukocytes and the total number of lymphocytes; among them, the absolute number of T helper lymphocytes (CD4+) decreases and the relative number of cytotoxic T lymphocytes (CD8+) increases; reversing the CD4+/CD8+ ratio, causing HIV in about 50% to 70% of infected patients. As a result, about 50% to 70% of infected patients develop HIV viremia and immune system damage, and therefore at-risk individuals may experience low lymphocyte counts during the latent phase of AIDS, as well as symptoms of upper respiratory tract infection such as fever, malaise, sore throat, and general malaise. However, the symptoms of early HIV infection are not specific and are very similar to other types of upper respiratory tract infections, so it is not possible to determine whether HIV infection is present. HIV infection can cause low lymphocytes, however, low lymphocytes alone cannot determine whether HIV infection is present because many other causes can cause similar low lymphocytes. The lymphocyte count is affected by both physiological and pathological factors, and the normal reference value is (0.8-4) × 10*9/L in adults. low lymphocytes include both absolute and relative decreases. Any of the various causes that lead to a significant increase in neutrophils can lead to a relative decrease in lymphocytes, when the lymphocyte ratio decreases, but the absolute number does not decrease, and there is no need to make a differential diagnosis for lymphocytes. Absolute decrease in lymphocytes is common for the following reasons in addition to AIDS: alkylating agents (cyclophosphamide, etc.) can cause a significant decrease in leukocytes, accompanied by a significant decrease in lymphocytes, and the decrease in lymphocytes can last for several years after stopping treatment; radiation therapy can destroy lymphocytes; lymphocyte decrease during recovery from influenza; immune diseases such as systemic lupus erythematosus, rheumatoid arthritis, mixed connective tissue diseases, polymyositis, etc., due to antibody production of anti-lymphocyte antibodies, resulting in the destruction of lymphocytes and the degree of reduction is related to the titer of the antibody; tuberculosis, early lymphopenia CD4+ cells are significantly reduced, if the treatment is effective, lymphocytes can be restored to normal; congenital immunodeficiencies such as severe combined immunodeficiency, ataxia capillaris, malnutrition or zinc deficiency, can cause lymphopenia to varying degrees. Certain drugs can also cause lymphopenia, such as nixic acid, cortisone, steroids, menadase, epinephrine, nitrogen mustard phenylbutyrate, and lithium. Therefore, HIV infection followed by HIV latency can cause low lymphocytes. However, low lymphocytes alone cannot determine if one is infected with HIV, as many other causes can cause similar low lymphocytes. To confirm the diagnosis of HIV infection, it is still necessary to combine the epidemiological history, clinical manifestations and laboratory tests in a concerted manner.