A person knows if his white blood cell count is normal by getting a complete blood count, according to Mayo Clinic. This test measures white blood cells, red blood cells, hemoglobin, hematocrit and blood platelets.
During a CBC, a white blood cell count of 3.5 to 10.5 billion cells per liter is considered normal, states Mayo Clinic. However, values that are a bit higher or lower do not necessarily mean the patient is ill. If the white blood cell count is far out of the normal range, it may indicate an illness. Someone whose white blood cell count is very low may have an autoimmune disease that is destroying the white blood cells or the bone marrow that produces it. It may also be a side effect of a drug or a complication of a malignancy.
A white blood cell count that's considerably higher than normal can mean that the patient is fighting off an infection, according to Mayo Clinic. As with a low white blood cell count, it could also mean an autoimmune disorder or that the body is reacting to a drug.
Another test for white blood cells is the white blood cell count, according to MedlinePlus. This test checks for different white blood cells, which include basophils, eosinophils, T and B cell lymphocytes, monocytes and neutrophils.