The complete blood count (CBC) is a screening test, used to diagnose and manage numerous diseases. It can reflect problems with fluid volume (such as dehydration) or loss of blood. It can show abnormalities in the production, life span, and destruction of blood cells. It can reflect acute or chronic infection, allergies, and problems with clotting.

The CBC test isolates and counts the six types of cells found in the blood: eosinophil, neutrophil, band cell, red blood cell, lymphocyte, and monocyte.

A CBC requires a simple blood drawing. Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand.

Preparation: There is no special preparation needed for this test.

How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. After the blood is drawn, there may be some throbbing.

There are a few slight risks associated with a CBC:

• Excessive bleeding
• Fainting or feeling lightheaded
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

Results:

Normal values vary with altitude and gender.

What abnormal results may mean:

Low numbers of red blood cells may indicate:

• Blood loss
• Anemia (various types)
• Hemorrhage
• Bone marrow failure (for example, from radiation, toxin, fibrosis, tumor)
• Erythropoietin deficiency (secondary to renal disease)
• Hemolysis (RBC destruction) from transfusion reaction
• Leukemia
• Multiple myeloma
• Malnutrition (nutritional deficiencies of iron, folate, vitamin B12, vitamin B6)
• Over hydration

Low numbers of white blood cells (leukopenia) may indicate:

• Bone marrow failure (for example, due to granuloma (granular tumor), tumor, or fibrosis)
• Presence of cytotoxic substance
• Collagen-vascular diseases (such as lupus erythematosus)
• Disease of the liver or spleen
• Radiation exposure

High numbers of white blood cells (leukocytosis) may indicate:

• Infectious diseases
• Inflammatory disease (such as rheumatoid arthritis or allergy)
• Leukemia
• Severe emotional or physical stress
• Tissue damage (for example, burns)

A low hematocrit may indicate:

• Anemia (various types)
• Blood loss (hemorrhage)
• Bone marrow failure (for example, due to radiation, toxin, fibrosis, tumor)
• Hemolysis (RBC destruction) related to transfusion reaction
• Leukemia
• Malnutrition or specific nutritional deficiency
• Multiple myeloma
• Over hydration
• Rheumatoid arthritis

A high hematocrit may indicate:

• Dehydration
• Burns
• Diarrhea
• Eclampsia
• Erythrocytosis
• Polycythemia vera
• Shock

Low hemoglobin values may indicate:

• Anemia (various types)
• Blood loss

High numbers of red blood cells may indicate:

• Low oxygen tension in the blood.
• Congenital heart disease.
• Cor pulmonale.
• Pulmonary fibrosis.
• Polycythemia vera.
• Dehydration (such as from severe diarrhea).
• Renal (kidney) disease with high erythropoietin production.