Complete Blood Cell (CBC) Count

This Blood Test Is Commonly Done For The Routine Management Of Many Conditions

Scientist holding microscope slide with blood droplet next to microscope
A red blood cell count is often done in the routine management of IBD and many other conditions.. Adam Gault/OJO Images/Getty Images

A complete blood cell (CBC) count is a comprehensive snapshot of the numbers, sizes, and types of blood cells present in the blood of a patient. A CBC count may be ordered as part of a general check-up, or to test for certain conditions, such as inflammation, infection, and anemia.

A CBC is actually comprised of several different tests that are run on the blood, including white blood cell counts and red blood cell counts, white blood cell differential, hemoglobin, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, red cell distribution width and platelet count.

How A Complete Blood Cell Count Is Done

A blood sample will be taken, normally from a vein in the arm. The blood is then sent to a clinical lab, where it is analyzed using a specialized machine. Sometimes, laboratory staff also review the appearance of blood cells manually, using a microscope.

How A Complete Blood Cell Count Is Used

The results of a CBC are used by physicians to check overall health status, response to a course of treatment, or more specific conditions, such as blood loss, infection, leukemia, sickle cell disease, or abnormal clotting.

Here are the parts of a CBC count and what they may show:

  • White blood cell count (WBC count). White blood cells are also called leukocytes. These cells are made in the bone marrow and are the ones that fight infection. Because more white blood cells are made when there is inflammation or an inflammatory process going on in the body, this could result in a higher than typical white blood cell count. This might be the case in people with IBD who are experiencing a flare-up of their disease. 
  • Red blood cell count (RBC count). The RBC count is the number of red blood cells in the blood. It's not a test that can tell a physician very much on its own, so it's usually done along with other tests. People with anemia will have a lower than typical red blood cell count. Anemia is often a problem for people with IBD.
  • WBC differential. There are several different types of WBCs in the blood. The WBC differential determines the number of each of these types of cells in the blood. Higher or lower levels could mean that some process in the body is causing an increase or decrease in one type of white blood cell. 
  • Hemoglobin. Hemoglobin is the "red" in the red blood cells. If hemoglobin is too low, the body won't be able to effectively transport enough oxygen to, and carbon dioxide from, the body's cells.
  • Hematocrit. The hematocrit is the level of red blood cells in a volume of blood. Low levels of hematocrit could be associated with IBD, especially if there is bleeding, or folate or B12 levels are low.
  • Mean corpuscular volume (MCV). The MCV is the average size of a red blood cell. If the RBC count is low, and hemoglobin is low, the MC is probably not within the normal range. 
  • Mean corpuscular hemoglobin (MCH). The MCH is an average of the hemoglobin per the red blood cells in a sample of blood. If red blood cells are bigger or smaller than typical, the MCH will be outside of the normal range.
  • Mean corpuscular hemoglobin concentration (MCHC). The MCHC is the average of the concentration of hemoglobin in the red blood cells. A level that's outside of the normal range could mean that there is more or less hemoglobin in the red blood cells than is typical. 
  • Red cell distribution width (RDW). RDW is a measure of size and volume of red blood cells. A higher RDW could mean that there's too much variation in red blood cell size.
  • Platelet count. Platelets are the part of blood that help it to clot and stop bleeding. When platelets are out of the normal range, there might be problems with clotting and bleeding.


American Association for Clinical Chemistry. "Complete Blood Count." Lab Tests Online. 25 Jun 2012. 9 Sept 2013.

Dugdale DC. "CBC." MedLine Plus. 19 Mar 2012. 9 Sept 2013.

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