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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.
Blood is a body fluid that has cells in 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 medications can also change their blood.
Blood cells have important jobs. The body has 3 main types:
A differential test gives even more information about the white blood cells that fight infection and disease.
Health care providers use the CBC with differential tests to:
Follow your health care provider’s instructions before the test. Tell them if your child is taking any:
These things may change the test results. If your child is only getting a complete blood count test (CBC), they might be able to eat and drink as normal. But if your doctor orders other blood tests, they might not be able to eat or drink.
A care team member inserts a needle into your child’s vein to get a blood sample and collects it in vials or tubes. They can also get blood from your child’s central venous access device such as a:
If your child does not have a device, the provider might start a peripheral IV to get blood samples.
The laboratory staff will study your child’s blood and report the results to your doctor.
CBC tests measure:
The number of cells, their size, and types in healthy person usually falls within a range of numbers (reference range or standard range). Your doctor compares your child’s results to normal reference ranges. Normal ranges can vary widely and depend on your child’s age. You should review these results with your health care provider who can explain what is normal for your child.
A complete blood count with a differential looks more closely at the types of white blood cells in the blood to study your child’s disease.
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, and leukopenia (low numbers of white blood cells, and blood cancers.
Reviewed: March 2022