A high percentage of monocytes may be normal, or it may be caused by infectious diseases, hematologic diseases and malignant tumors. 1. Normal phenomenon: Normal children’s monocytes can be slightly higher than adults, and infants within two years of age can also have significantly higher monocytes, which is a normal phenomenon and usually does not require special treatment. 2. Infectious diseases: for example, infective endocarditis, black fever, recovery from acute infections and active tuberculosis, etc., may increase the percentage of monocytes. 3. Hematologic diseases: For example, mononuclear cell leukemia, recovery from granulocyte deficiency, myelodysplastic syndrome, chronic granulomonocytic leukemia and other hematologic diseases are very likely to increase the percentage of monocytes. 4. Malignant tumors: patients suffering from malignant tumors such as lymphoma, lung cancer and stomach cancer may also have a high monocyte percentage. When patients find that the monocyte percentage is high, they should go to the hospital in time and under the guidance of the doctor, undergo the relevant examination to clarify the cause of the disease and treat it in time.