A white blood cell count (WBC) is a blood test that measures the number of white blood cells in the blood, also known as leukocytes. It is a part of a complete blood count (CBC) and is used to diagnose conditions such as infections, allergic reactions, inflammation, and blood cancer such as leukemia or lymphoma. The normal number of WBCs in the blood is 4,500 to 11,000 WBCs per microliter (4.5 to 11.0 × 109/L) . However, normal value ranges may vary slightly among different labs, and some labs use different measurements or may test different specimens. Therefore, it is important to talk to your healthcare provider about your test results. A low number of WBCs is called leukopenia, and a count less than 4,500 cells per microliter (4.5 × 109/L) is below normal. A higher than normal WBC count is called leukocytosis, and it may be due to certain drugs or medicines, infections, inflammatory disease, leukemia or Hodgkin disease, tissue damage, or pregnancy.