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Complete Blood Count (CBC) (cont.)

Why Are Complete Blood Count Tests Used?

Patient Comments

Uses of the complete blood count are extensive. In general, the complete blood count can be done as part of routine health exam and general screening by a doctor. It may be ordered if an infection or anemia is suspected. It may also be ordered to evaluate abnormal bleeding.

As mentioned earlier, an elevation of the white blood cell count or an abnormality of the white blood cell differential may be suggestive of an infection or inflammation. A high or a low white blood cell count could also be a sign of underlying cancer such as leukemia or lymphoma.

A low red blood cell or hemoglobin count typically indicates anemia (low blood). Anemia, typically seen as low hemoglobin or low hematocrit on the complete blood count, is a sign of an underlying disease and it is not a disease itself. Anemia can have many causes including blood loss, bone marrow problems, nutritional deficiencies, genetic hemoglobin structural or functional problems (sickle cell or thalassemia), or kidney failure. These are only the most common causes of anemia, and the list of all causes of anemia is very extensive. Anemia found in a complete blood count may be suggestive of ongoing slow blood loss and, therefore, can be used to detect cancers, such as colon cancer. If anemia is detected, usually the MCV and RDW give some additional clues as to the possible causes of anemia.

A low platelet count (thrombocytopenia) may also be detected in the complete blood count. This may be due to bone marrow problems, some medications or excessive alcohol use, immunologic or genetic problems, advanced liver disease, or cancers such as leukemia. The MPV may indicate how rapidly platelets are made in the bone marrow and released into the blood stream. A high platelet count may also be suggestive of an inflammation or blood malignancy, such as leukemia and lymphoma.

Medically reviewed by John A. Daller, MD; American Board of Surgery with subspecialty certification in surgical critical care


Bonilla, Francisco A, MD, PhD, and E Richard Stiehm, MD. "Laboratory evaluation of the immune system." Updated Dec 2, 2015.

Medically Reviewed by a Doctor on 10/24/2016

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