The total number of white blood cells (leukocytes) in a sample of blood. White blood cells are part of the immune system, made in the bone marrow, and help fight infection and other diseases. The count combines all five major types (neutrophils, lymphocytes, monocytes, eosinophils, basophils); a separate blood differential breaks down each type. WBC is usually reported as part of a complete blood count (CBC).
To help diagnose or monitor conditions linked to a high or low white cell count. It may be ordered for signs of infection (fever, chills, body aches, a red or non-healing wound, persistent cough), or signs of inflammation or an autoimmune disease. It is also used to monitor people whose condition or medicine weakens the immune system, for example checking whether the count is dropping too low during chemotherapy. Newborns and children may be tested for routine screening or a suspected white-cell disorder.
As a general adult reference point, MedlinePlus states the normal number of WBCs is 4,500 to 11,000 per microliter (4.5 to 11.0 x 10^9/L). This VARIES by lab, and by age and sex — newborns and young children normally run higher than adults. The same source cautions that normal value ranges may vary slightly among different labs, some of which use different measurements or specimens. Always compare your result to the reference range printed on your own report.
A higher-than-normal count (leukocytosis) has many possible causes and is not a diagnosis by itself. Reported causes include infections (often bacterial), inflammatory diseases such as rheumatoid arthritis, allergic reactions, tissue damage from a burn or surgery, and less commonly blood cancers such as leukemia or Hodgkin disease. Everyday factors can also raise it without serious illness — smoking, physical or emotional stress, pregnancy, certain medicines (for example corticosteroids), or having had the spleen removed. It is a signal to look further, interpreted alongside symptoms and other tests.
A lower-than-normal count (leukopenia) also has many possible causes and must be read in context. Reported causes include bone marrow problems (from infection, disease, or scarring), cancers that damage the bone marrow, cancer treatments such as chemotherapy or radiation, autoimmune disorders such as lupus (SLE), liver or spleen disease, some viral illnesses such as mononucleosis, and HIV. Certain medicines can lower it (for example some antibiotics, anticonvulsants, and diuretics). A low count can also reflect a harmless inherited/ethnic trait. Usually interpreted alongside other tests.
Reference ranges vary by laboratory, age, sex, and method — the range on your own report is what applies to you. A single value out of range doesn’t confirm any condition; your clinician interprets it alongside your symptoms, history, and other results. This page is general information, not medical advice.
General reference, not medical advice, and not a substitute for your clinician. Lab reference ranges and interpretation depend on the laboratory and on your individual situation — discuss your results with a licensed healthcare professional.