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To evaluate the number of red blood cells (RBCs); to screen for, help diagnose, or monitor conditions affecting red blood cells
As part of a complete blood count (CBC), during a health checkup, or when a healthcare practitioner suspects that you have a condition such as anemia (decreased number of RBCs) or polycythemia (increased number of RBCs)
A blood sample drawn from a vein in your arm or by a fingerstick (children and adults) or heelstick (newborns)
Red blood cells (RBCs), also called erythrocytes, are cells that circulate in the blood and carry oxygen throughout the body. The RBC count totals the number of red blood cells that are present in your sample of blood. It is one test among several that is included in a complete blood count (CBC) and is often used in the general evaluation of a person's health.
Blood is made up of a few different types of cells suspended in fluid called plasma. In addition to RBCs, there are white blood cells (WBCs) and platelets. These cells are produced in the bone marrow and are released into the bloodstream as they mature. RBCs typically make up about 40% of the blood volume. RBCs contain hemoglobin, a protein that binds to oxygen and enables RBCs to carry oxygen from the lungs to the tissues and organs of the body. RBCs also help transport a small portion of carbon dioxide, a waste product of cell metabolism, from those tissues and organs back to the lungs, where it is expelled.
The typical lifespan of an RBC is 120 days. Thus the bone marrow must continually produce new RBCs to replace those that age and degrade or are lost through bleeding. A number of conditions can affect RBC production and some conditions may result in significant bleeding. Other disorders may affect the lifespan of RBCs in circulation, especially if the RBCs are deformed due to an inherited or acquired defect or abnormality. These conditions may lead to a rise or drop in the RBC count. Changes in the RBC count usually mirror changes in other RBC tests, including the hematocrit and hemoglobin level.
A red blood cell (RBC) count is typically ordered as part of a complete blood count (CBC) and may be used as part of a health checkup to screen for a variety of conditions. This test may also be used to help diagnose and/or monitor a number of diseases that affect the production or lifespan of red blood cells.
An RBC count is ordered as a part of the complete blood count (CBC), often as part of a routine physical or as part of a pre-surgical workup. A CBC may be ordered when you have signs and symptoms suggesting a disease that might affect red blood cell production. Some common signs and symptoms associated with anemia that generally lead to a healthcare practitioner ordering a CBC are:
Some signs and symptoms that may appear with a high RBC count include:
A CBC may also be performed on a regular basis to monitor people who have been diagnosed with conditions such as:
Since an RBC count is performed as part of a complete blood count (CBC), results from other components are taken into consideration. A rise or drop in the RBC count must be interpreted in conjunction with other tests, such as hemoglobin, hematocrit, reticulocyte count, and/or red blood cell indices.
The following table summarizes what results may mean.
|Test||Reference Range||Examples of Causes of Low Result||Examples of Causes of High Result|
|Red Blood Cell Count (RBC)||
Men: 4.5-5.9 x 106/microliter
Women: 4.1-5.1 x 106 microliter
Men: 4.5-5.9 x 1012/L
Women: 4.1-5.1 x 1012/L
Known as anemia
Known as polycythemia
from Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed.
McPherson R, Pincus M, eds. Philadelphia, PA: Elsevier Saunders; 2011.
Note: Conventional Units are typically used for reporting results in U.S. labs;
SI Units are used to report lab results outside of the U.S.
Some causes of a low RBC count (anemia) include:
Some causes of a high RBC count (polycythemia) include:
Your RBC count is interpreted by your healthcare practitioner within the context of other tests that you have had done as well as other factors, such as your medical history. A single result that is slightly high or low may or may not have medical significance. There are several reasons why a test result may differ on different days and why it may fall outside a designated reference range.
A test value that falls outside of the established reference range supplied by the laboratory may mean nothing significant. Generally, this is the case when the test value is only slightly higher or lower than the reference range and this is why a healthcare practitioner may repeat a test on you and why they may look at results from prior times when you had the same test performed.
However, a result outside the range may indicate a problem and warrant further investigation. Your healthcare provider will consider your medical history, physical exam, and other relevant factors to determine whether a result that falls outside of the reference range means something significant for you. For more, read the articles on Reference Ranges and What They Mean.
An RBC count can be used to detect a problem with red blood cell production and/or lifespan, but it cannot determine the underlying cause. In addition to the full CBC, some other tests may be performed at the same time or as follow up to help establish a diagnosis. Examples include:
First, a healthcare practitioner must determine the cause of someone's abnormal RBC count so the appropriate treatment can be prescribed. For some anemias, treatment may include a dietary supplement or a change in diet to include nutritional foods. In some instances, it may only require a change in the person's current medication. For more severe cases, treatment may involve transfusion with blood from a donor. For some, prescribing a drug to stimulate red cell production in the bone marrow may be required, especially for people who have received chemotherapy or radiation treatments.
Maybe. Some healthcare practitioners' offices are equipped with laboratory instruments and staffed by trained laboratorians who are able to perform this test.
Yes, to the extent that if you eat a well-balanced diet, you can prevent anemia due to a lack of iron, vitamin B12, or folate in the foods you eat. Sometimes use of a supplement is recommended if you are at risk of a vitamin deficiency. However, the most common cause of vitamin B12 deficiency is malabsorption, and the most common cause of iron deficiency is bleeding. These conditions and other RBC problems that are caused by diseases other than nutritional deficiencies will not be corrected by diet.
Fatigue and weakness may indicate a low or high RBC count. Fainting, pallor, shortness of breath, dizziness, and/or altered mental status can also indicate a low RBC count. Disturbed vision, headache, and flushing may be present with increased numbers of RBCs.
A recent blood transfusion can affect results of an RBC count.
Alteration of the number of RBCs is often temporary and can be easily corrected and/or returned to normal levels by treating and resolving the underlying condition.
During pregnancy, body fluids tend to accumulate, thus decreasing the RBC count in relation to fluid volume.
Living at high altitudes causes an increase in RBC count; this is the body's response to the decreased oxygen available at these heights.
Women tend to have slightly lower RBC counts than men.
Sources Used in Current Review
Wintrobe's Clinical Hematology. 12th ed. Greer J, Foerster J, Rodgers G, Paraskevas F, Glader B, Arber D, Means R, eds. Philadelphia, PA: Lippincott Williams & Wilkins: 2009, Section 2: The Erythrocyte.
Harmening, D. Clinical Hematology and Fundamentals of Hemostasis, Fifth Edition, F.A. Davis Company, Philadelphia, 2009, Chapter 3.
Sources Used in Previous Reviews
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Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Chap 31.
(March 1, 2011) National Heart, Lung and Blood Institute. What is Polycythemia vera? Available online at http://www.nhlbi.nih.gov/health/public/blood/index.htm. Accessed Sep 2011.
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