Reticulocytes
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- Also Known As:
- Retic Count
- Reticulocyte Percent
- Reticulocyte Index
- Corrected Reticulocyte
- Reticulocyte Production Index
- RPI
- Formal Name:
- Reticulocyte Count

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At a Glance
Why Get Tested?
To help your health care practitioner evaluate your 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?
When results of a complete blood count (CBC) show you have a low RBC count, hemoglobin, and hematocrit and/or when you have symptoms of anemia; when your health care practitioner wants to evaluate your bone marrow function
Sample Required?
A blood sample is collected by inserting a needle into a vein in your arm or sometimes from a fingerstick or heelstick (infant).
Test Preparation Needed?
None
What is being tested?
Reticulocytes are newly produced, relatively immature red blood cells (RBCs). A reticulocyte count helps to determine 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. Reticulocytes are visually, slightly larger than 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. 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 is continually producing 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.
Higher than normal percentage of reticulocytes: 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 or to treatment of deficiency anemias (such as iron deficiency anemia or pernicious anemia) 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.
Lower than normal percentage of reticulocytes: 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, cirrhosis, kidney disease, 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 blood 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.
Some drugs may increase or decrease reticulocyte counts.
Common Questions
View Sources
Sources Used in Current Review
2020 Review performed by Michelle Moy, M.Ad. Ed., MT (ASCP) SC, Assistant Professor and Program Director, Biomedical Science/Medical Lab Science, College of Arts and Sciences, Madonna University.
© 2020 Mayo Medical Laboratories. Reticulocytes, Blood. Available online at https://www.mayocliniclabs.com/test-catalog/Clinical+and+Interpretive/9108. Accessed April 2020.
Elaine M. Keohane PhD MLS(ASCP)SHCM (Author), Catherine N. Otto PhD MBA MLS(ASCP)CM SH DLM (Author), Jeanine M. Walenga PhD MLS(ASCP)HCM (Author). Rodak’s Hematology: Clinical Principles and Applications 6th Edition pls 164-166.
(Updated November 26, 2019) Maakaron, J. What is the role of reticulocyte count in the workup of anemia? Medscape Reference. Available online at https://www.medscape.com/answers/198475-155081/what-is-the-role-of-reticulocyte-count-in-the-workup-of-anemia. Accessed April 2020.
Sources Used in Previous Reviews
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(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’.
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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.
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.
Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 820-821.
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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. 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. Accessed on 11/23/08.
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. 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. Accessed January 2013.
(Updated: Nov 4, 2011) Maakaron J. Anemia. Medscape Reference article. Available online at http://emedicine.medscape.com/article/198475-overview. Accessed January 2013.
Szigeti, R. and Curry, C. (2014 September 5, Updated). Reticulocyte Count and Reticulocyte Hemoglobin Content. Medscape Drugs & Diseases [On-line information]. Available online at http://emedicine.medscape.com/article/2086146-overview. Accessed 07/18/15.
Peerschke, E. (2014). Using the Hemoglobin Content of Reticulocytes (RET-He) to Evaluate Anemia in Patients With Cancer. Medscape News & Perspective. Am J Clin Pathol. 2014;142(4):506-512. [On-line information]. Available online at http://www.medscape.com/viewarticle/833778. Accessed 07/18/15.
Keohane, E, Smith, L. and Walenga, J. (© 2016). Rodak’s Hematology Clinical Principles and Applications 5th Edition: Elsevier Saunders, Saint Louis, MO. Pp 145.
2016 review by Christina Nickel, MHA, MLS(ASCP)cm, Laboratory Quality Manager, Bryan Medical Center.
Kohnle D. Reticulocyte Count. Health Library: Evidence-Based Information [serial online]. February 2015. Available from: Nursing Reference Center Plus, Ipswich, MA. Accessed February 1, 2016.
Piva E, Brugnara C, Spolaore F, Plebani M. Clinical utility of reticulocyte parameters. Clinics In Laboratory Medicine [serial online]. March 2015;35(1):133-163. Available from: Medline, Ipswich, MA. Accessed February 1, 2016.
Simionatto M, de Paula J, do Nascimento A, et al. Manual and automated reticulocyte counts. Hematology [serial online]. December 2010;15(6):406-409. Available from: Academic Search Premier, Ipswich, MA. Accessed February 1, 2016.
Van Leeuwen A, Bladh M. Reticulocyte Count. Davis’s Comprehensive Handbook of Laboratory & Diagnostic Tests with Nursing Implications, 6th ed [e-book]. Philadelphia, Pennsylvania: F.A. Davis Company; 2015. Available from: Nursing Reference Center Plus, Ipswich, MA. Accessed February 1, 2016.
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