Monocytes are a type of human leukocyte. Generally, monocytes account for 3%-8% of all leukocytes, below 3% is monocyte reduction, above 8% is monocyte increase, monocyte reduction generally has no obvious clinical significance. Monocyte increase is common in two situations: first, when viral infections, the number of monocytes will appear a certain increase, such as the common clinical infectious mononucleosis, is due to EBV infection caused by the increase in the number of monocytes. Second, certain hematologic disorders can also show a significant increase in monocyte percentage, the most common being acute monocytic leukemia, where an abnormally high percentage of monocytes can eventually be found in the peripheral blood due to disorderly proliferation of monocytes, often accompanied by anemia and thrombocytopenia. Monocyte elevation alone has little effect on the body, but if it is accompanied by symptoms such as anemia and bleeding, one should be alert to the possibility of acute leukemia.