A low white blood cell count (leukopenia) is a decrease in disease-fighting cells (leukocytes) in your blood. Leukopenia is almost always related to a decrease in a certain type of white blood cell (neutrophil).

The definition of low white blood cell count varies from one medical practice to another. In general, for adults a count lower than 4,000 white blood cells per microliter of blood is considered a low white blood cell count. For children, that threshold varies with age.

Some people who are otherwise healthy have white cell counts that are lower than what's usually considered normal, but which are normal for them.


White blood cells are manufactured in bone marrow — the spongy tissue inside some of your larger bones. A low white blood cell count usually is caused by:

  1. Viral infections that temporarily disrupt the work of bone marrow
  2. Certain disorders present at birth (congenital) that involve diminished bone marrow function
  3. Cancer or other diseases that damage bone marrow
  4. Autoimmune disorders that destroy white blood cells or bone marrow cells
  5. Severe infections that use up white blood cells faster than they can be produced
  6. Medications, such as antibiotics, that destroy white blood cells
  7. Sarcoidosis (collections of inflammatory cells in the body)

Specific causes of a low white blood cell count include:

  1. Aplastic anemia
  2. Chemotherapy
  4. Hypersplenism (an abnormality of the spleen causing blood cell destruction)
  5. Kostmann's syndrome (a congenital disorder involving low production of neutrophils)
  6. Leukemia
  7. Lupus
  8. Malnutrition and vitamin deficiencies
  9. Myelodysplastic syndromes
  10. Myelokathexis (a congenital disorder involving failure of neutrophils to enter the bloodstream)
  11. Radiation therapy
  12. Rheumatoid arthritis and other autoimmune disorders
  13. Tuberculosis (and other infectious diseases)