Complete Blood Count (CBC) Test

What is a complete blood count test?

Benefits of a CBC test

A CBC can help your care team: 

• Check your child’s overall health 
• Look for signs of infection, anemia, blood disorders, or cancer 
• Monitor disease or medical condition 
• See how well treatments or medicines are working  
• Check how well the immune system is working 

What a CBC test measures

A CBC test measures:

• Red blood cells (RBCs): Carry oxygen through the body. Low levels can cause anemia, which may lead to fatigue or shortness of breath. 
  
• White blood cells (WBCs): Help fight infection. Low levels can increase the risk of infection. 
  
• Platelets: Help the blood clot and stop bleeding. Low levels (thrombocytopenia) may cause easy bruising or bleeding. 
  
• Hemoglobin:  Carries oxygen to the body’s tissues and organs. Low levels can be a sign of anemia.
  
• Hematocrit (HCT): Shows how much of the blood is made up of red blood cells. Results can help identify anemia and other conditions. This is also called packed cell volume (PCV).
  
• Mean corpuscular volume (MCV): Measures the average size of red blood cells. The results help show if your child has certain types of anemia.

Getting ready for a CBC test

Follow your care team’s instructions before the test. 

• Most CBC tests do not require fasting (not eating or drinking). Most foods do not affect CBC test results. But they could affect other blood tests.  Your child may need to fast if they are having other blood tests at the same time. 
• Tell your care team about anything your child is taking, including:
  • Prescription and over-the-counter medicines
  • Vitamins, minerals, and other supplements
  • Herbal products

Talk to your care team if you have questions.

What to expect during the CBC test

A health care provider will take a small amount of your child’s blood from a vein. If your child has a central line, the provider may use it to take the sample. 

After the CBC test

You usually get the CBC results within a few days. The report shows your child’s results and a range of numbers called a reference range. These numbers show what is considered normal. Your child’s care provider compares the results with these ranges. Ranges vary based on your child’s age, sex, and other factors.  

Talk with your care team about your child’s results. They can explain what the numbers mean for your child.  

Possible risks of a CBC test

A CBC test is simple and generally safe. But your child may have:

• Pain or discomfort where the needle goes in
  
• Mild bleeding or bruising  
  
• Feeling dizzy or lightheaded
  
• A very small risk of infection
  

Questions to ask your care team

• Why does my child need a CBC test? 
• What does a CBC check for? 
• Which CBC results are most important for my child's condition or treatment? 
• How should my child prepare for the CBC test? 
• When and how will we get the results of the CBC test? 
• Are any of my child's CBC results outside the expected range? 
• What do the CBC results mean for my child? 
• Will my child need more tests or follow-up care? 

Related Content