Leukemia can be suspected with white blood cells over 20 x 10^9/L, but leukemia is not determined by a single test of white blood cell count. Possible causes of elevated white blood cells are infectious diseases (e.g., acute tonsillitis, acute bronchitis, acute pneumonia, acute appendicitis), major trauma (e.g., postoperative, burns), poisoning, and leukemia. The basis of leukemia diagnosis includes medical history, clinical manifestations (such as anemia, fever, abnormal bleeding, lumps appearing in the neck and axilla or groin), and a comprehensive analysis of bone marrow aspiration, pathological diagnosis, and cytogenetic examination is also needed to make a clear diagnosis. Therefore, although leukemia can cause elevated white blood cells, it cannot be judged solely on the basis of this test, because there are many diseases that cause elevated white blood cells, and leukemia is only one of them.