Common causes of high lymphocyte percentage in adults include viral infections, tuberculosis infections, acute and chronic lymphocytic leukemia, etc. It can also be seen in other diseases that cause relative elevation of the index, such as rheumatoid arthritis. Lymphocyte percentage refers to the ratio of lymphocyte count to the total number of white blood cells. The high value may be due to the increase in the absolute value of lymphocytes, or it may be due to the decrease in the absolute values of neutrophils, eosinophils, basophils and monocytes in the classification of white blood cells, which leads to the relative increase in the percentage of lymphocytes, but the absolute value of lymphocytes is normal. 1. When the body is infected with viruses (adenovirus, EBV, etc.) or Mycobacterium tuberculosis, as well as acute and chronic lymphocytic leukemia, the absolute lymphocyte values may be mildly elevated, resulting in a high lymphocyte ratio. 2. When there is a decrease in the counts of neutrophils, eosinophils, basophils and monocytes, the lymphocyte ratio may be relatively elevated, but the lymphocyte count is not significantly elevated. This may occur in humans with rheumatologic diseases such as dry syndrome and rheumatoid arthritis. In the event of an elevated lymphocyte ratio, it is necessary to consult a hematologist in a timely manner to determine the specific cause of the disease and then treat the cause of the disease under the direction of a physician.