At a Glance
Why Get Tested?
To evaluate the number of red blood cells (RBCs); used to screen for, help diagnose, or monitor conditions affecting red blood cells
When to Get Tested?
As part of a complete blood count (CBC), during a health examination, or when your doctor 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)
Test Preparation Needed?
The Test Sample
What is being tested?
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 a person's sample of blood. It is one test among several that is included in a complete blood count (CBC), which 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 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. There are a number of conditions that can affect the production of new RBCs and/or their lifespan, in addition to those conditions that may result in significant bleeding. These conditions may lead to a rise or drop in the RBC count.
Changes in the RBC count usually mirror changes in the hematocrit and hemoglobin level. When the values of the RBC count, hematocrit, and hemoglobin decrease below the established reference interval, the person is said to be anemic. When the RBC and hemoglobin values increase above the normal range, the person is said to be polycythemic. Too few RBCs can affect the amount of oxygen reaching the tissues, while too many RBCs can make the blood thicker, causing slowed blood flow and related problems.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm or by collecting blood from a fingerstick (for children and adults) or a heelstick (for newborns).
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
Ask a Laboratory Scientist
This form enables you to ask specific questions about your tests. Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, American Society for Clinical Laboratory Science. If your questions are not related to your lab tests, please submit them via our Contact Us form. Thank you.
* indicates a required field
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
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 through http://www.nhlbi.nih.gov. Accessed Sep 2011.
(Aug 1, 2010) National Heart, Lung and Blood Institute. Anemia. Available online at http://www.nhlbi.nih.gov/health/health-topics/topics/anemia/ through http://www.nhlbi.nih.gov. Accessed Sep 2011.
(June 17, 2011) Conrad M. Anemia. Medscape Reference article. Available online at http://emedicine.medscape.com/article/198475-overview through http://emedicine.medscape.com. Accessed Sep 2011.
(August 26, 2011) Harper J. Pediatric Megaloblastic Anemia. eMedicine article. Available online at http://emedicine.medscape.com/article/959918-overview throughhttp://emedicine.medscape.com. Accessed Sep 2011.
(June 8, 2011) Artz A. Anemia in Elderly Persons. eMedicine article. Available online at http://emedicine.medscape.com/article/1339998-overview throughhttp://emedicine.medscape.com. Accessed Sep 2011.
(February 9, 2010) Dugdale D. RBC Count. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003644.htm. Accessed Sep 2011.
Riley R, et.al. Automated Hematologic Evaluation. Medical College of Virginia, Virginia Commonwealth University. Available online at http://www.pathology.vcu.edu/education/PathLab/pages/hematopath/pbs.html#Anchor-Automated-47857 through http://www.pathology.vcu.edu. Accessed Sep 2011.
Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL eds, (2005). Harrison's Principles of Internal Medicine, 16th Edition, McGraw Hill, Pp 329-336.
Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006, Pp 447-448.
Harmening D. Clinical Hematology and Fundamentals of Hemostasis. Fifth Edition, F.A. Davis Company, Piladelphia, Chapter 3.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
Hillman RS and Finch CA. Red Cell Manual (1974). FA Davis, Philadelphia. Pp. 23-51.
Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp. 797-799.