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Complete Blood Count Test with Differential in Children

What is a complete blood count test with differential?

Graph showing structure of blood with red blood cells at bottom at 41%, white blood cells in middle making up about 4%, and plasma on top at 55%

Blood is a liquid in the body that contains red blood cells, white blood cells, platelets, and plasma.

A complete blood count (CBC) test with differential measures the number and types of white blood cells in the blood.

Blood cells have important jobs. The body has 3 main types:

  • Red blood cells that carry oxygen through the body
  • White blood cells that help fight infection and disease
  • Platelets that help form blood clots after injury

A CBC test measures many aspects of the blood. A CBC with differential gives more details about white blood cells.

Blood contains blood cells and a liquid called plasma, made of water and proteins.

Children with infections, cancers, or blood disorders have changes in the number and kind of cells and proteins in their blood. Therapies and medicines can also change their blood.

Benefits of a CBC with differential

Health care providers use the CBC with differential to:

  • Diagnose a medical problem
  • Check if your child has an infection
  • Tell how your child fights infection
  • Study how a disease affects their body
  • Tell if a treatment is working 

Getting ready for a CBC test

Follow your health care team’s instructions before the test. Tell them if your child is taking any:

  • Medicines (both prescribed and those without prescription)
  • Vitamins
  • Herbal products

These things may change the test results.

If your child is only getting a CBC test, they might be able to eat and drink as normal. But they might not if your care team orders other blood tests.

Regular CBC tests help the care team monitor the patient’s health and ability to fight off infections.

Regular CBC tests help the care team monitor the patient’s health and ability to fight off infections.

Steps of a CBC test

A care team member inserts a needle into your child’s vein to get a blood sample. They collect it in vials or tubes. The care team can also get blood from your child’s central venous access device such as a:

If your child does not have a device, the care team might start a peripheral IV to get blood samples.

Lab staff will study your child’s blood and report the results to your doctor.

What a CBC test measures

A CBC test measures:

  • Red blood cells (RBCs) – The numbers, size, and types of red blood cells
  • White blood cells (WBCs) – The numbers and types of white blood cells. The normal white blood cell count in healthy people is 5,000 to 10,000/mm3.
  • Platelets – The numbers and size of the platelets. A normal platelet count in healthy people is 150,000 to 400,000/mm3.
  • Hemoglobin – An iron-rich protein in red blood cells that carries oxygen to the body’s tissues. A normal hemoglobin level in healthy people is 12 g/dL.
  • Hematocrit (HCT or PCV) – How much space red blood cells take up in the blood compared to plasma and other cells
  • Reticulocyte count – The number of young red blood cells in the blood
  • Mean corpuscular volume (MCV) – The average size of red blood cells

The number of cells, their size, and types in a healthy person usually falls within a range of numbers (reference range or standard range). Your doctor compares your child’s results to these ranges.

Normal ranges can vary. They depend on your child’s age. Review these results with your care team. They can explain what is normal for your child.

What a CBC with differential measures

A CBC with differential includes more information about your child’s white blood cells.

Types of white blood cells

Types of blood cells and related conditions

Low numbers or abnormalities of certain types of blood cells can lead to health conditions that require treatment such as:

  • Anemia
  • Blood clotting disorders
  • Bleeding disorders
  • Leukopenia (low numbers of white blood cells and blood cancers)
  • Thrombocytopenia (low numbers of platelets in the blood)

Key points about a CBC with differential

  • A complete blood count test (CBC) measures the number and types of cells in the blood.
  • A CBC test can also measure some proteins made by the blood cells, such as hemoglobin.
  • A CBC with differential gives details about the types and numbers of white blood cells.
  • These tests are useful for the diagnosis of disease and to see how well treatments are working.

Reviewed: March 2023