About the Test
Purpose of the test
A reticulocyte count is used to determine the number and/or percentage of reticulocytes in the blood to help evaluate conditions that affect RBCs, such as anemia or bone marrow disorders. Reticulocytes are newly produced, relatively immature RBCs. They form and mature in the bone marrow before being released into the blood.
The reticulocyte count may be used:
- As a follow-up to abnormal results on a complete blood count (CBC), RBC count, hemoglobin, or hematocrit, to help determine the cause
- To determine if the bone marrow is functioning properly and responding adequately to the body’s need for RBCs
- To help detect and distinguish between different types of anemia
- To monitor response to treatment, such as that for iron-deficiency anemia
- To monitor bone marrow function following treatments such as chemotherapy
- To monitor bone marrow function following a bone marrow transplant
Most often, a reticulocyte count is performed with an automated instrument (hematology analyzer) and can be done simultaneously with a CBC, which includes an RBC count, hemoglobin, and hematocrit. Either an absolute number of reticulocytes and/or a percentage of reticulocytes of total RBC count can be reported, although the absolute number is more commonly reported.
What does the test measure?
RBCs 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 is a good indicator of the ability of your bone marrow to adequately produce RBCs (erythropoiesis).
RBCs typically survive for about 120 days in circulation, and the bone marrow continually produces 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 reticulocyte count: 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 releasing RBCs sooner into the blood before they become more mature.
When this happens, the number and percentage of reticulocytes in the blood increase until a sufficient number of RBCs replaces those that were lost or until the production capacity of the bone marrow is reached. Reticulocyte count is also higher than normal when a patient with iron deficiency anemia or megaloblastic anemia (due to vitamin B12 deficiency) is treated with supplementary iron or vitamin B12.
Lower than normal reticulocyte count: 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 or leukemia.
Diminished production can also be due to other factors, for example, chronic 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 increased production of erythropoietin, disorders that cause chronic overproduction of RBCs (polycythemia vera), and cigarette smoking.
Some drugs may increase or decrease reticulocyte counts.
When should I get this test?
A reticulocyte count may be ordered when:
- CBC results show a decreased RBC count and/or a decreased hemoglobin and hematocrit
- A health care practitioner wants to evaluate bone marrow function
- You have signs and symptoms of anemia or chronic bleeding, such as paleness, lack of energy, fatigue, weakness, shortness of breath, and/or blood in the stool
- You have been diagnosed and are being treated for a condition known to affect RBC production, such as iron deficiency anemia, vitamin B12 or folate deficiency, or kidney disease (which can affect the production of erythropoietin, a hormone created by the kidneys that stimulates RBC production by the bone marrow)
- You are undergoing radiation or chemotherapy
- You have received a bone marrow transplant
- Occasionally when you have an increased number of RBCs and elevated hemoglobin and hematocrit, to help determine the degree and rate of overproduction of RBCs
Finding a Reticulocyte Count Test
How can I get a reticulocyte count test?
Your doctor usually orders this test to evaluate your bone marrow’s ability to produce RBCs and help distinguish between various causes of anemia. The test also monitors 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.
You can also order a reticulocyte count test online without a doctor’s order.
Can I take the test at home?
While you can purchase a reticulocyte count test at home, you will need to visit a laboratory to have your blood sample taken.
How much does the test cost?
How much a reticulocyte count test costs depends on several factors. Where you have your blood sample taken and your level of health insurance coverage will affect your overall costs. For the best estimate of the costs for a test prescribed by your doctor, reach out to your doctor or health insurance company.
Taking a Reticulocyte Count Test
Reticulocyte count testing involves having a blood sample taken from a vein in your arm.
Before the test
While there are generally no special preparations you need to take before your test, follow any instructions provided with your online test or by your doctor.
During the test
A lab technician will insert a needle into a vein in one of your arms to withdraw a vial of blood. This process usually involves minimal pain, although some people experience burning or stinging at the injection site. The total blood draw usually lasts only a few minutes.
After the test
Once you have had the test, the technician will bandage the puncture site to stop any bleeding. Generally you can return to normal activities when the test is over, although the lab technician will let you know if there are any restrictions you should follow. You may feel slight pain or bruising at the injection site, but this is normally temporary.
Reticulocyte Count Test Results
Receiving test results
Reticulocyte count test results are normally available within a few business days of the lab receiving your sample. You may receive your results in the mail or through an online health portal.
Your doctor may contact you to discuss your results and schedule a follow-up appointment.
Interpreting test results
Results must be interpreted carefully and along with results of other tests, such as an RBC count, hemoglobin (Hb), hematocrit (Hct), or a full CBC. In general, the reticulocyte count (absolute number or percentage) reflects recent bone marrow activity.
The results may indicate whether a disease or condition is present that is generating an increased demand for new RBCs and whether the bone marrow can respond to the extra requirement. Occasionally, results may indicate the overproduction of RBCs.
When anemia is present (i.e., low RBCs, low hemoglobin, low hematocrit) and the bone marrow is responding appropriately to the demand for increased numbers of RBCs, the bone marrow will produce more and allow for the early release of more immature RBCs, increasing the number of reticulocytes in the blood.
A high reticulocyte count with low RBCs, low hemoglobin, and low hematocrit (anemia) may indicate conditions such as:
- Bleeding: If you bleed, then the number of reticulocytes will rise a few days later in an attempt to compensate for the red cell loss. And if you have chronic blood loss, the number of reticulocytes will stay at an increased level as the marrow tries to keep up with the demand for new RBCs (although it may not be high if the blood loss eventually leads to iron deficiency).
- Hemolytic anemia: In this condition, anemia is caused by increased destruction of RBCs due to various causes. The bone marrow increases RBC production to compensate, resulting in a high reticulocyte count.
- Hemolytic disease of the newborn: This condition causes increased RBC destruction, similar to hemolytic anemia described above.
A low reticulocyte count with low RBCs, low hemoglobin, and low hematocrit (anemia) may be seen, for example, with:
- Iron deficiency anemia (untreated)
- Pernicious anemia or folic acid deficiency (untreated)
- Aplastic anemia
- Chemotherapy radiation therapy
- Bone marrow failure caused by infection or cancer involving bone marrow
- Severe kidney disease; this may cause a low level of erythropoietin
- Alcoholism
Reticulocyte count used to be reported as a calculated percentage or index when they were manually counted from a stained blood smear. Nowadays, the reticulocyte count is reported as an absolute number (for example, thousands per microliter) because they are counted by automated laboratory equipment.
The reticulocyte test indicates the presence of a disease or condition but is not directly diagnostic of any one particular disease. It is a sign that further investigation may be necessary and a tool that can be used to monitor the effectiveness of therapy.
If reticulocyte numbers rise following chemotherapy, a bone marrow transplant, or treatment of an iron or vitamin B12 or folate deficiency, bone marrow RBC production is beginning to recover.
When you do not have anemia or have a high RBC count (polycythemia), a high reticulocyte count may indicate an overproduction of RBCs. Some conditions that may cause this include:
- Polycythemia vera, a type of blood cancer
- Tumor that produces erythropoietin
When you talk with your doctor, some of these questions may be helpful to review:
- Were my results high, low, or normal?
- If my results were too high or too low, what is the most likely cause?
- Were any other measurements taken along with my reticulocyte count? If so, were they normal or abnormal?
- Are there any follow-up tests that you recommend?
Sources
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Maakaron JE, Taher AT, Conrad ME. Anemia. In: Besa EC. Medscape. Updated September 27, 2021. Accessed December 21, 2022. https://www.medscape.com/answers/198475-155081/what-is-the-role-of-reticulocyte-count-in-the-workup-of-anemia
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National Heart, Lung, and Blood Institute. Hemolytic Anemia. Updated March 24, 2022. Accessed December 21, 2022. http://www.nhlbi.nih.gov/health/dci/Diseases/ha/ha_whatis.html.
Peerschke EIB, Pessin MS, Masiak P. Using the Hemoglobin Content of Reticulocytes (RET-He) to Evaluate Anemia in Patients With Cancer. Medscape. Date unknown. Accessed December 21, 2022. http://www.medscape.com/viewarticle/833778
Szigeti RG, Curry CV. Reticulocyte Count and Reticulocyte Hemoglobin Content. In: Hermelin D, ed. Medscape. Updated June 1, 2022. Accessed December 21, 2022. http://emedicine.medscape.com/article/2086146-overview
