At a Glance
Why Get Tested?
To help evaluate the bone marrow's ability to produce red blood cells (RBCs); to help distinguish between various causes of anemia; to help monitor bone marrow response and the return of normal marrow function following chemotherapy, bone marrow transplant, or post-treatment follow-up for iron deficiency anemia, vitamin B12 or folate deficiency anemia, or renal failure
When to Get Tested?
A blood sample obtained by inserting a needle into a vein in your arm or sometimes from a fingerstick or heelstick (infant)
Test Preparation Needed?
The Test Sample
What is being tested?
Reticulocytes are newly produced, relatively immature red blood cells (RBCs). This test determines the number and/or percentage of reticulocytes in the blood and is a reflection of recent bone marrow function or activity.
Red blood cells are produced in the bone marrow where blood-forming (hematopoietic) stem cells differentiate and develop, eventually forming reticulocytes and finally becoming mature RBCs. Unlike most other cells in the body, mature RBCs have no nucleus, but reticulocytes still have some remnant genetic material (RNA). As reticulocytes mature, they lose the last residual RNA and most are fully developed within one day of being released from the bone marrow into the blood. Normally, less than 2% of the RBCs in circulation are reticulocytes. The reticulocyte count or percentage is a good indicator of the ability of a person's bone marrow to adequately produce red blood cells (erythropoiesis).
RBCs typically survive for about 120 days in circulation, and the bone marrow must continually produce new RBCs to replace those that age and degrade or are lost through bleeding. Normally, a stable number of RBCs is maintained in the blood through continual replacement of degraded or lost RBCs.
A variety of diseases and conditions can affect the production of new RBCs and/or their survival, in addition to those conditions that may result in significant bleeding. These conditions may lead to a rise or drop in the number of RBCs and may affect the reticulocyte count.
For example, acute or chronic bleeding (hemorrhage) or increased RBC destruction (hemolysis) can lead to fewer RBCs in the blood, resulting in anemia. The body compensates for this loss by increasing the rate of RBC production and by releasing RBCs sooner into the blood, before they become more mature. When this happens, the number and percentage of reticulocytes in the blood increases until a sufficient number of RBCs replaces those that were lost or until the production capacity of the bone marrow is reached.
Decreased RBC production may occur when the bone marrow is not functioning normally. This can result from a bone marrow disorder such as aplastic anemia. Diminished production can also be due to other factors, for example, radiation or chemotherapy treatments for cancer, a low level of the hormone erythropoietin, or deficiencies in certain nutrients such as iron, vitamin B12, or folate. Decreased production leads to fewer RBCs in circulation, decreased hemoglobin and oxygen-carrying capacity, a lower hematocrit, and a reduced number of reticulocytes as old RBCs are removed from the bloodstream but not fully replaced.
Occasionally, both the reticulocyte count and the RBC count will be increased because of excess RBC production by the bone marrow. This may be due to an increased production of erythropoietin, disorders that cause chronic overproduction of RBCs (polycythemia vera), and cigarette smoking.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm or sometimes from pricking a finger or the heel of an infant.
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
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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
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 331-336.
Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Pp 487, 491-492.
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, Pp 782-785.
(2010) Piva E, Brugnara C, Chiandetti L, Plebani M. Automated reticulocyte counting: state of the art and clinical applications in the evaluation of erythropoiesis. Clin Chem Lab Med. 2010 Oct;48(10):1369-80. Available online at http://www.ncbi.nlm.nih.gov/pubmed/20666695 through http://www.ncbi.nlm.nih.gov. Accessed January 2013.
(Updated: May 24, 2012) Szigeti, R. Reticulocyte Count and Reticulocyte Hemoglobin Content. Medscape Reference article. Available online at http://emedicine.medscape.com/article/2086146-overview through http://emedicine.medscape.com. Accessed January 2013.
(Updated: Nov 4, 2011) Maakaron J. Anemia. Medscape Reference article. Available online at http://emedicine.medscape.com/article/198475-overview through http://emedicine.medscape.com. Accessed January 2013.
Sources Used in Previous Reviews
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
Irwin, J. and Kirchner, J. (2001 October 15). Anemia in Children. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20011015/1379.html through http://www.aafp.org.
Nanda, R. (2005 February 1, Updated). Reticulocyte count. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003637.htm.
(2004 Summer). Immature Reticulocyte Fraction(IRF). The Pathology Center Newsletter v9(1). [On-line information]. Available online at http://www.thepathologycenter.org/Newsletters/Newsletter3r.pdf#search='reticulocyte' through http://www.thepathologycenter.org.
(1998 June 15). Reticulocyte Counts. American Society of Clinical Oncology, Idaho LMRP [On-line information]. Available online at http://www.asco.org/ac/1,1003,_12-002393-00_18-0018894,00.asp?state=ID through http://www.asco.org.
Check, W. (2002 June). Perks plus: the new hematology analyzers. College of American Pathologists [On-line journal]. Available online at http://www.cap.org/apps/docs/cap_today/feature_stories/hematology_analyzers_feature.html through http://www.cap.org.
Brill, J. and Baumgardner, D. (2000 November 15). Normocytic Anemia. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20001115/2255.html through http://www.aafp.org/afp/20001115/2255.html.
Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 820-821.
Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp 952-955.
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Levin, M. (2007 March 8, Updated). Reticulocyte Count. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003637.htm. Accessed on 11/23/08.
Kahsai, D. and van Roekens, C. (2007 July 26). Anemia, Acute. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.emedicine.com/emerg/TOPIC808.HTM. Accessed on 11/23/08.
Abrahamian, B. and Wilke, E. (2008 January 14, Updated). Anemia, Chronic. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.emedicine.com/emerg/TOPIC734.HTM. Accessed on 11/23/08.
(2006 September). What is Hemolytic Anemia? National Heart Lung and Blood Institute [On-line information]. Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/ha/ha_whatis.html through http://www.nhlbi.nih.gov. Accessed on 11/23/08.
(2007 December). What is Aplastic Anemia? National Heart Lung and Blood Institute [On-line information]. Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/aplastic/aplastic_whatis.html through http://www.nhlbi.nih.gov. Accessed on 11/23/08.