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. White blood cells help fight infections, and a WBC count is often ordered 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 lower than normal WBC count may be due to certain medications, bone marrow disease, or infections caused by bacteria or viruses. It may also be due to inflammatory disease, tissue damage, or blood cancer such as leukemia or lymphoma.

A high white blood cell count (leukocytosis) is usually considered to be anything above 11,000 cells per μl of blood in an adult. This can be related to infections, bone marrow disease, or medications.

It is important to note that test results may vary depending on age, gender, health history, and other factors. Pregnant individuals and children under two may have ranges that differ from those of adults. If you have a low WBC count, your doctor may want to do additional tests to determine the underlying cause and develop an appropriate treatment plan.