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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, including anemia, infections, and leukemia, in your blood. It can help see how your overall health is.

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

  • Number and types of white blood cells. Your body has five types of white blood cells, all of which help fight infections. The white blood cell (WBC) count, including WBC differential, counts each type of white blood cell: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. High numbers of white blood cells may mean you have inflammation or an infection somewhere in your body.

  • Number of red blood cells. Too few red blood cells may be a sign of anemia or other diseases. In rare cases, too many may cause problems with blood flow.

  • Variation in the size of your red blood cells. You may have greater variation in red blood cell size if you have anemia.

  • Hematocrit. This is the percentage of red blood cells in a certain volume of whole blood. It measures how much of your blood is made up of red blood cells. Low hematocrit may be a sign of anemia from excessive bleeding or other causes, and higher hematocrit can stem from dehydration or other disorders.

  • Hemoglobin value. Hemoglobin is the red 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.

  • Platelet count. Platelets play a role in blood clotting. Too few platelets may mean you have a problem with excess bleeding.

  • 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 and, among other things, may mean your body is low on vitamin B12 or folate. If your red blood cells are smaller, this can be a sign of certain types of anemia, such as anemia because of iron deficiency.

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

Why do I need this test?

You may need this test if your doctor suspects that you have a blood disorder. You may need this test if you have:

  • Unusual bleeding or bruising

  • Signs of infection or inflammation

  • Persistent weakness and tiredness that your doctor suspects may be caused by anemia

You may also get this test as part of a routine checkup. The test may also be used to see if certain treatments are working.

What other tests might I have along with this test?

Your doctor may also order other tests if your results for this test are abnormal. These tests may include a blood smear, bone marrow evaluation, spinal fluid analysis, and C-reactive protein test.

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: 3.3 to 8.7 thousand per cubic milliliter (thousand/mm3)

  • Platelets: 147 to 347 thousand/mm3

  • Hemoglobin: 12.6 to 16.1 grams per deciliter (g/dL)

  • Hematocrit: 38 to 47.7 percent; the normal percentage depends on gender and age

Depending on your results, you may have:

  • Anemia. A low red blood cell count may lead to this finding.

  • Erythrocytosis. Your doctor may diagnose you with this if your hematocrit value is high, meaning your red blood cells make up an unhealthy proportion of your blood count.

  • Neutropenia. You may have this if your white blood cell count is low, which puts you at risk for infections.

  • Leukocytosis. When your WBC count is elevated, your doctor may diagnose you with leukocytosis. In rare cases, leukemia is the cause.

  • Thrombocytosis. This is a high platelet count, which may be caused by iron deficiency, inflammatory disorders, and splenectomy.

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 doctor 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 doctor 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.