Complete Blood Count

Definition
Purpose
Description
Precautions
Side effects
Interactions

Definition

A complete blood count (CBC) provides important information about the types and numbers of cells in the blood; in particular, information about red blood cells, white blood cells and platelets.

Purpose

The purpose of a CBC is to help physicians to diagnose conditions related to abnormalities in the blood such as infections and anemia.

Description

A complete blood count usually includes the following elements:

• Red blood cell count (also called RBC or erythrocyte count)

• Red blood cell indices - mean corpuscular volume (MCV, mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC)
• Hemoglobin (also called Hgb)
• Hematocrit (also called HCT)
• White blood cell count (also called WBC or leukocyte count)
• Platelet count (also called thrombocyte count)

Red blood cells (erythrocytes) transport oxygen between the lungs and cells throughout the rest of the body. They also transport carbon dioxide back to the lungs so it can be exhaled. A low red cell count may be due to anemia and cells in the body may not be getting the oxygen that they need. A red blood cell count that is abnormally high may be due to an uncommon condition called polycythemia.

White blood cells (leukocytes) protect the body against infection. When an infection develops, white blood cells attack and destroy the pathogen (bacteria,

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?

• A complete blood count is typically ordered by a family doctor, internist or surgeon but any physician may order one.
• A blood sample is usually obtained by a nurse, phlebotomist or medical technologist.
• The blood sample is tested or processed by a medical technologist.
• Results are usually reviewed, returned to the person being tested and interpreted by the physician initially ordering the complete blood count.

virus, or other organism) causing it. White blood cells are larger than red blood cells but fewer in number. When a person has a bacterial infection, the number of white cells increases very quickly. The number of white blood cells is sometimes used to pinpoint an infection or to see how the body is reacting to cancer treatment.

Platelets (thrombocytes) are the smallest type of blood cell. They are essential to the process of blood clotting. When bleeding occurs, platelets swell, clump together, and form a sticky plug that helps to stop the bleeding. If the platelet count is too low, uncontrolled bleeding may occur. If the platelet count is too high, there is a chance of a blood clot forming in a blood vessel. Platelets may contribute to the process of hardening of the arteries (atherosclerosis).

There are three red blood cell indices: mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC). They are measured by a laboratory instrument machine that calculates their values from other measurements in a complete blood count. The mean corpuscular volume reflects the average size of red blood cells. The mean corpuscular hemoglobin value reflects the quantity of hemoglobin in an average red blood cell. The mean corpuscular hemoglobin concentration reflects the concentration of hemoglobin in an average red blood cell. These numbers are used in diagnosing different types of anemia.

The hemoglobin value reflects the amount of hemoglobin in blood and is a good measure of the ability of a person’s blood stream to carry oxygen throughout the

QUESTIONS TO ASK YOUR DOCTOR

• Why is a complete blood count needed?
• What do the results indicate for my health?
• What treatment options do I have?

body. A hemoglobin molecule comprises much of he volume of red blood cells. It carries oxygen and gives red blood cells their normal color.

The hematocrit value reflects the amount of space (volume) that red blood cells occupy in the blood. The value is given as a percentage of red blood cells in a volume of blood. For example, a hematocrit of 46 means that 46% of the blood’s volume is comprised of red blood cells. Males and females have different normal hematocrit values.

Normal values for the elements of a complete blood count include the following:

• Red blood cell (erythrocyte) count: 4.2-5.9 million
• White blood cell (leukocyte) count: 4,300-10,800
• Platelet (thrombocyte) count: 150,000-400,000
• Mean corpuscular volume (MCV): 86-98
• Mean corpuscular hemoglobin (MCH): 27-32
• Mean corpuscular hemoglobin concentration (MCHC): 32-36%
• Hemoglobin (Hgb): 13-18 for men and 12-16 for women
• Hematocrit (HCT): 45–52% for men and 37–48% for women

A complete blood count can be ordered at any time.

Precautions

Precautions are generally not needed for a complete blood count.

At the time of drawing blood, the only precaution needed is to clean the venipuncture site with alcohol.

Side effects

The most common side effects of a complete blood count are minor bleeding (hematoma) or bruising at the site of venipuncture.

KEY TERMS

Hematoma— A collection of blood that has entered a closed space.

Phlebotomist— Health care professional trained to obtain samples of blood.

Interactions

There are no interactions for a complete blood count.

Resources

BOOKS

Fischbach, F. T. and M. B. Dunning. A Manual of Laboratory and Diagnostic Tests. 8th ed. Philadelphia: Lippincott Williams & Wilkins, 2008.

McGhee, M. A Guide to Laboratory Investigations. 5th ed. Oxford, UK: Radcliffe Publishing Ltd, 2008.

Price, C. P. Evidence-Based Laboratory Medicine: Principles. Practice, and Outcomes. 2nd ed. Washington, DC: AACC Press, 2007.

Scott, M.G., A. M. Gronowski, and C. S. Eby. Tietz’s Applied Laboratory Medicine. 2nd ed. New York: Wiley-Liss, 2007.

Springhouse, A. M.. Diagnostic Tests Made Incredibly Easy! 2nd ed. Philadelphia: Lippincott Williams & Wilkins, 2008.

PERIODICALS

Amati, L., M. Chiloiro, E. Jirillo, and V. Covelli. “Early pathogenesis of atherosclerosis: the childhood obesity.” Current Pharmaceutical Design 13, no. 36 (2007): 3696–3700.

James, T. R., H. L. Reid, and A. M. Mullings. “Are published standards for haematological indices in pregnancy applicable across populations: an evaluation in healthy pregnant Jamaican women.” BMC Pregnancy and Childbirth 8, no. 1 (2008): 8–19.

Liao, S. C., M. F. Yang, and I. N. Lee. “Transforming laboratory data to improve medical care for patients with chronic kidney disease.” Journal of Nephrology 21, no. 1 (2008): 74–80.

Lippi, G., A. Bassi, G. P. Solero, G. L. Salvagno, and G. C. Guidi. “Prevalence and type of preanalytical errors on inpatient samples referred for complete blood count.” Clinical Laboratory 53, no. 9-12 (2007): 555–556.

ORGANIZATIONS

American Association for Clinical Chemistry. http://www.aacc.org/AACC/.

American Society for Clinical Laboratory Science. http://www.ascls.org/.

American Society of Clinical Pathologists. http://www.ascp.org/.

College of American Pathologists. http://www.cap.org/apps/cap.portal.

OTHER

American Clinical Laboratory Association. “Information about clinical chemistry.” 2008 [cited February 24, 2008]. http://www.clinical-labs.org/.

Clinical Laboratory Management Association. “Information about clinical chemistry.” 2008 [cited February 22, 2008]. http://www.clma.org/.

Lab Tests On Line. “Information about lab tests.” 2008 [cited February 24, 2008]. http://www.labtestsonline.org/.

National Accreditation Agency for Clinical Laboratory Sciences. “Information about laboratory tests.” 2008 [cited February 25, 2008]. http://www.naacls.org/.

L. Fleming Fallon, Jr, MD, DrPH

Computerized axial tomography seeCT scans