What does it mean when your doctor or nurse practitioner orders a CBC on your blood?

The complete blood count (CBC) is a series of lab tests that gives important information about the main elements of the blood. These include the WBC, or white blood count, the RBC, or red blood count, and the platelets. It also includes the hemoglobin and hematocrit.

Each of these components is valuable in its own way to determine the diagnosis of many disorders and conditions, and also to monitor them, once they’ve been diagnosed. Symptoms such as fatigue, weakness, infection, or bruising are just some of the many reasons to do a CBC.

A brief description of each component:

WBC (white blood count or leukocyte count): White blood cells are disease-fighting cells that protect the body against infection.A high white cell count, or leukocytosis, often occurs when infection anywhere in the body sets in, as the white cells try to fight it. Normally the white cell count is approximately 4,000-10,000. Lower than normal white cell counts are also referred to as leukopenia. Some medications, including chemotherapy, can lower the WBC. Some viral infections can also lower the white cell count, as can toxic reactions to chemicals.

The WBC is further broken down by categorizing the white cells into groups which include neutrophils, lymphs, monos, basophils and eosinophils. This is called the white cell differential. Valuable information is obtained when searching for a diagnosis as each type of white cell has its own purpose in the blood.

RBC (red cell count): Red blood cells carry oxygen from the lungs to the rest of the body. With a low red cell count, the oxygen level to the body is less than is needed. This results is anemia, which can be treated in various ways, depending on the type of anemia. Severe anemia may require a blood transfusion. Increased red cells, or polycythemia, can also be a problem, making it difficult for the oxygen to move from the lungs to the body.

Hemoglobin: a molecule in the red cells that is the vehicle for the transportation of oxygen.

Hematacrit: measures the amount of space taken up by the blood cells. The hematacrit and the hemoglobin are good indicators of anemia or polycythemia.

Platelets: the smallest blood cells, are also called thrombocytes. Too few platelets are known as thrombocytopenia, while too many are called thrombocytosis. Platelets are necessary for clotting of the blood. Too few can cause abnormal bleeding, while too many can be responsible for blood clots forming in the blood vessels.

There are many situations where a CBC is necessary. It can be part of a routine check-up, a follow-up to monitor treatment, or part of an evaluation based on a patient’s symptoms.