The normal range for white blood cell (WBC) count for a child varies according to age and, at certain ages, the sex of the child.

A white blood cell (WBC) count reflects the number of these immune system cells circulating in your child's bloodstream. A WBC count is usually performed as part of a complete blood count (CBC), which includes other tests such as a red blood cell count, platelet count, and hemoglobin and hematocrit levels, among others. The normal range for a total WBC count is somewhat higher in children than adults and varies according to a child's age.


WBC counts are naturally at their highest level in the newborn period. Levels typically decline significantly during the first month after birth and then continue to decline more gradually for the remainder of the child's first and second year. Normal values vary slightly from one testing laboratory to another. The reference ranges for WBC count established by Mayo Medical Laboratories for infants from birth to 2 years are as follows 1:

  • Birth: 9.0 to 30.0 x 109/L
  • 1 to 7 days: 9.4 to 34.0 x 109/L
  • 8 to 14 days: 5.0 to 21.0 x 109/L
  • 15 days to 1 month: 5.0 to 20.0 x 109/L 
  • 2 to 5 months: 5.0 to 15.0

    x 109/L * 6 months to 2 years old: 6.0 to 11.0 x 109/L  

Toddlers, Children and Adolescents

WBC counts for children after they reach their second birthday vary slightly based on age, and sex for children aged 6 to 15. The reference ranges for WBC count established by Mayo Medical Laboratories for toddlers, children and adolescents are as follows 1:

  • 2 years old: 5.0 to 12.0 x 109/L  
  • 3 to 5 years old: 4.0 to 12.0 x 109/L  
  • 6 to 11 years old, males: 3.4 to 9.5 x 109/L  
  • 6 to 11 years old, females: 3.4 to 10.8

    x 109/L   12 to 15 years old, males: 3.6 to 9.1 x 109/L     12 to 15 year old, females: 4.1 to 8.9 x 109/L   * 16 years and older, males and females: 3.5 to 10.5

    x 109/L  


WBCs are immune system cells. The 5 different types of WBCs include neutrophils (also known as polymorphonuclear leukocytes or PMNs), lymphocytes, monocytes, eosinophils and basophils. Each type of WBC has a different function. Neutrophils and lymphocytes are the most abundant WBCs. Children normally have more lymphocytes than neutrophils, though this predominance switches to primarily neutrophils after about age 8. A WBC count includes all of the different types of WBCs. A high WBC count is called leukocytosis and a low count is called leukopenia. There are many possible causes of an abnormal WBC count in a child.

High WBC Count

Many conditions and circumstances can cause a high WBC count in a child. Most increases are transient but others indicate a more serious underlying problem. Examples of causes of leukocytosis in a child include:

  • Infection
  • Vigorous exercise
  • Seizures
  • Allergic reaction
  • Corticosteroid medication use, such as for asthma
  • Hereditary anemia, such as sickle cell disease
  • Inflammatory bowel disease
  • Down syndrome
  • Leukemia

Low WBC Count

A low WBC count in a child is less common than an elevated count. Some of the potential causes of a low WBC count in children include:

  • Severe infection, especially bacterial
  • Nutritional deficiencies, such as vitamin B12 and/or folate
  • Leukemia and other bone marrow abnormalities
  • Spleen enlargement

Other Considerations

Other tests usually included in a CBC help your doctor narrow the list of possible causes if your child has an abnormal WBC count. This additional information includes counts and relative proportions of the different types of WBCs, and examination of WBCs under the microscope. In many cases, an abnormality in a child's WBC count is temporary, such as with a viral or bacterial illness. Talk with your doctor if you have questions or concerns about your child's WBC count.

Reviewed and revised by: Tina M. St. John, M.D.