What is a CBC? Blood Test Basics


The doctor looks down at his clipboard and says, “We’ll have a CBC done and go from there.” You know it has something to do with your blood being tested…but for what exactly? Blood tests can help detect an underlying disease or medical condition that may be causing your symptoms. Some can even tell how well an organ is functioning. But what does a CBC test for and how is the test performed?

What is a CBC?

CBC stands for Complete Blood Count. The test provides the level of three different types of cells in the blood:

  1. Red blood cells: the cells that transport oxygen throughout your body
  2. White blood cells: the cells that help fight off infections
  3. Platelets: the cells that help clot blood to stop bleeding

Why Would My Doctor Request a CBC Test for My Child?

If your child isn’t feeling well, a Complete Blood Count test can help rule out medical conditions like anemia, infections, and inflammation.

Can My Child Eat or Drink Before a CBC?

Unlike glucose testing, which requires patients to fast, your child should be able to eat and drink unless the doctor orders other blood tests that require fasting. Because certain medications can impact test results, it’s also important to inform your child’s doctor about any supplements or medications your child is taking.  Blood transfusions and smoking can also impact test results, so alert the doctor about those factors too.

How Is a CBC Performed?

A CBC test is taken just like most other blood tests, with a small amount of blood drawn from a vein with a needle, typically from the inside of the elbow or back of the hand. For babies, sometimes the blood is drawn from the heel. If you’re concerned about how your child will react to having blood drawn, ask the doctor’s office for a pediatric-friendly blood lab in the area.

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