Lower than the normal amount of white blood cells.

A low white blood cell count, or leukopenia, is a decrease in disease-fighting cells (leukocytes) circulating in your blood.

The threshold for a low white blood cell count varies from one medical practice to another. A count lower than 3,500 white blood cells per microliter of blood is generally considered a low white blood cell count. The threshold for a low white blood cell count in children varies with age and sex.

A low white blood cell count is usually found when your doctor has ordered tests to help diagnose a condition you're already experiencing. It's rarely an unexpected finding or simply discovered by chance. Talk to your doctor about what these results mean. A low white blood cell count and along with results from other tests may already indicate the cause of your illness, or your doctor may suggest other tests to further assess your condition.

Because a chronic very low white blood cell count makes you vulnerable to infections, discuss precautions to avoid contracting contagious diseases with your doctor. You may be advised to wear a face mask and avoid anyone with a cold or other illness, and you may be reminded to wash your hands regularly and thoroughly.

Al low white blood cell count usually is caused by one of the following:

  • Viral infections that temporarily disrupt bone marrow function
  • Congenital disorders characterized by diminished bone marrow function
  • Cancer or other diseases that damage bone marrow
  • Autoimmune disorders that destroy white blood cells or bone marrow cells
  • Overwhelming infections that use up white blood cells faster than they can be produced
  • Drugs that destroy white blood cells or damage bone marrow

Specific causes of low white blood cell count include:

  • Aplastic anemia
  • Certain medications, such as antibiotics and diuretics
  • Chemotherapy
  • Hypersplenism, a premature destruction of blood cells by the spleen
  • Hyperthyroidism (overactive thyroid)
  • Infectious diseases
  • Kostmann's syndrome, a congenital disorder involving low neutrophil production
  • Leukemia
  • Lupus
  • Myelodysplastic syndromes
  • Myelofibrosis
  • Myelokathexis, a congenital disorder involving failure of neutrophils to enter the bloodstream
  • Other autoimmune disorders
  • Other congenital disorders
  • Parasitic diseases
  • Radiation therapy
  • Rheumatoid arthritis
  • Vitamin deficiencies


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