Many blood tests measure the amount of certain chemicals or proteins in your child’s blood, but a complete blood count checks the blood cells themselves. It measures the numbers of different types of blood cells, their sizes, and their appearance. It is a very common and useful blood test.
In general, the test measures 3 main components of blood:
The CBC test may be done to check your child’s overall health. It may also be done to check if your child has:
Usually no preparation is needed for this test.
For newborns, a blood sample is taken from the heel. For older children, a small amount of blood is taken with a fingerstick, or from the arm with a needle.
The blood is collected in tubes and sent to a lab. The lab measures the amounts of the different components in the sample of blood. The blood sample may also be viewed with a microscope to double check the different kinds of white blood cells.
Having this test will take just a few minutes. There is no risk of getting AIDS, hepatitis, or any other blood-borne disease from this test.
The normal ranges for the different kinds of blood cells measured vary based on your child’s age. These ranges may vary slightly from lab to lab. Normal ranges are usually shown next to your child’s results in the lab report.
Some of the reasons your child’s red blood cell count may be higher than normal are:
A red blood cell count or hemoglobin level lower than normal is called anemia. The size of the red blood cells gives an important clue to possible causes of anemia:
Some of the reasons your child’s white blood cell count may be higher than normal are:
Your child’s white blood cell count may be lower than normal if your child has a viral infection, including the common cold or is taking chemotherapy.
Your child’s platelet count may be higher than normal if your child has an autoimmune disease, such as rheumatoid arthritis or Crohn's disease. The platelet count can also increase with viral infections, but will go back to normal as your child recovers.
Some of the reasons your child’s platelet count may be lower than normal are:
Test results are only one part of a larger picture that takes into account your child’s medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your child’s healthcare provider about your child’s result and ask questions.
If your child’s test results are not normal, ask your child’s healthcare provider: