Health Encyclopedia

Complete Blood Count with Differential

Does this test have other names?

CBC w/ diff

What is this test?

This panel of tests looks for many illnesses in your blood. These include anemia, infections, and leukemia. It can help see how your overall health is.

The test gets a lot of information from your blood sample:

  • The number and types of white blood cells (WBCs). Your body has 5 types of white blood cells. All play a role in fighting infections. High numbers of WBCs, or of a specific type of WBC, may mean you have an infection or inflammation somewhere in your body. Low numbers of WBCs may mean you are at risk for infections.

  • The number of red blood cells (RBCs). RBCs carry oxygen throughout the body and remove excess carbon dioxide. Too few RBCs may be a sign of anemia or other diseases. In rare cases, too many may cause problems with blood flow.

  • How the size of your red blood cells varies. This test is known as red cell distribution width (RDW). For instance, you may have greater differences in red blood cell size if you have anemia.

  • Hematocrit. This means the portion of red blood cells in a certain amount of whole blood. A low hematocrit may be a sign of too much bleeding. Or it might mean that you have iron deficiency or other disorders. A higher than normal hematocrit can be caused by dehydration or other disorders.

  • Hemoglobin. Hemoglobin is a protein in red blood cells. It carries oxygen from your lungs to the rest of the body. Abnormalities can be a sign of problems ranging from anemia to lung disease.

  • The average size of your red blood cells. This test is known as mean corpuscular volume (MCV). MCV goes up when your red blood cells are bigger than normal. This happens if you have anemia caused by low vitamin B12 or folate levels. If your red blood cells are smaller, this can mean other types of anemia, such as iron deficiency anemia.

  • A platelet count. Platelets are cell fragments that play a role in blood clotting. Too few platelets may mean you have a higher risk of bleeding. Too many may mean a number of possible conditions.

  • Mean corpuscular hemoglobin. This test measures how much hemoglobin your red blood cells have.

Why do I need this test?

You may need this test if your healthcare provider thinks you have a blood disorder. You may need this test if you have:

  • Unusual bleeding or bruising

  • Infection or inflammation

  • Weakness and tiredness that doesn’t go away. These may be symptoms of anemia

You may also have this test if your healthcare provider thinks you may have a certain disease or condition. Or you may have this test as part of a routine exam to check your health. The test may also be used to see how well certain treatments are working.

What other tests might I have along with this test?

Your healthcare provider may also order other tests if your results for this test are abnormal. These may include other blood tests, urine tests, and bone marrow or spinal fluid tests.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Normal ranges for the different parts of a CBC are:

  • Red blood cells: 3.93 to 5.69 million per cubic millimeter (million/mm3)

  • White blood cells: 4.5 to 11.1 thousand per cubic milliliter (thousand/mm3)

  • Platelets: 150 to 450 thousand/mm3

  • Hemoglobin: 11.7 to 16.1 grams per deciliter (g/dL) in women, 13.2 to 17.3 in men

  • Hematocrit: 34% to 46% in women, 36% to 52% in men

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Certain medications might affect your results, so talk with your healthcare provider about the medicines you are taking.

How do I get ready for this test?

You don't need to prepare for this test. But be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.



Medical Reviewers:

  • Hanrahan, John, MD
  • Sather, Rita, RN