Also Known As
Retic Count
Reticulocyte Index
Corrected Reticulocyte
Formal Name
Reticulocyte Count
This article was last reviewed on
This article waslast modified on
6 February 2018.
At a Glance
Why Get Tested?

To help evaluate the bone marrow's ability to produce red blood cells (RBCs) and to help distinguish between anaemia related to blood loss or destruction and anaemia related to decreased RBC production; 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 anaemia

When To Get Tested?

When you have a decreased (or increased) RBC count, haemoglobin, haematocrit or platelet count and your doctor wants to evaluate bone marrow activity

Sample Required?

A blood sample obtained by inserting a needle into a vein in the arm or sometimes from pricking a finger or the heel in the case of infants.

Test samples are collected into sample tubes containing EDTA preservatives.

Test Preparation Needed?

No test preparation is needed. Blood sample can be collected at any time of the day, before or after a meal.

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you will be able to access your results online.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, gender, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

Reticulocytes are immature red blood cells (RBCs). They are produced in the bone marrow when stem cells differentiate and progress toward RBC development, eventually forming reticulocytes and finally mature RBCs. Most RBCs are fully mature before they are released from the bone marrow into the blood, but about 0.5 – 2% of the RBCs in circulation will be reticulocytes. This test measures the number and percentage of reticulocytes in the blood and serves as an indicator of the adequacy of bone marrow red blood cell (RBC) production.

Normal RBCs have a lifespan of about 120 days. The body attempts to maintain a stable number of RBCs in circulation by continually removing old RBCs and producing new ones in the bone marrow. If this steady state is disrupted by an increased loss of RBCs or by decreased production, then anaemia will develop. Increased loss of red blood cells may be due to severe and short term (acute) or chronic bleeding haemorrhage) or haemolysis. The body compensates for this loss by increasing the rate of RBC production. When this happens, the number and percentage of reticulocytes in the blood increases until a sufficient number of RBCs is present and the balance is restored or until the production capacity of the marrow is reached.

Decreased RBC production may occur when the bone marrow is not functioning normally, due to a bone marrow disorder such as aplastic anaemia or due to marrow suppression from a variety of causes including radiation and chemotherapy treatments for cancer, because of insufficient erythropoietin, or because of deficiencies in certain nutrients such as iron, vitamin B12, or folate. This decreased production leads to fewer RBCs in circulation, decreased haemoglobin and oxygen-carrying capacity, a lower  haematocrit, and to a reduction in the 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. This may be due to a variety of causes including inappropriately increased production of erythropoietin, disorders that chronically produce increased numbers 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.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed. Blood sample can be collected at any time of the day, before or after a meal.

Accordion Title
Common Questions
  • How is it used?

    The reticulocyte count is used to help determine if the  bone marrow is responding adequately to the body’s need for red blood cells (RBCs) and to help determine the cause of and classify different types of anaemia. The number of reticulocytes must be compared to the number of RBCs to calculate a percentage of reticulocytes and haemoglobin and/or haematocrit are also usually requested to help evaluate the severity of anaemia.

    The RBC, haemoglobin, and haematocrit are frequently measured as part of a full blood count (FBC). The FBC usually includes an evaluation of red blood cells (RBCs), White blood cells (WBCs) and Platelets (PLT) characteristics, such as cell size, volume, and shape. Based on these results, a reticulocyte count may be requested to further examine the RBCs. Reticulocytes can be distinguished from mature RBCs because they still contain remnant genetic material (RNA), a characteristic not found in mature RBCs which do not contain genetic material. Circulating reticulocytes generally lose their RNA within one to two days, thus becoming mature RBCs.

  • When is it requested?

    A reticulocyte count may be requested when you have a decreased RBC count and/or a decreased haemoglobin and haematocrit and your doctor wants to evaluate bone marrow function. If you have no apparent symptoms, these findings may be found during routine blood testing. Reticulocyte count may also be used when you have symptoms such as paleness, tiredness, weakness, shortness of breath, and/or blood in the stool.

    A Reticulocyte count is useful after a recent episode of blood loss or in cases where the lifespan of red cell is shortened as seen in some haemolytic anaemia.

    Reticulocyte count may also be used when you have a known iron or vitamin  vitamin B12 or folate deficiency, known kidney disease, known bone marrow suppression as may occur during chemotherapy or bone marrow transplant. Reticulocyte count may be requested with a RBC count, haematocrit, and haemoglobin at intervals recommended by your doctor to monitor marrow function and response to treatment.

    When you have an increased number of RBCs and elevated haemoglobin and haematocrit, the reticulocyte count may be used to help work out the degree and rate of overproduction of RBCs.

  • What does the test result mean?

    What your doctor is looking for is an appropriate response from the bone marrow, to confirm that your bone marrow is working properly to an increased demand for red blood cells. In a healthy patient, the reticulocyte percentage is stable. When the number of RBCs and haematocrit decreases, the percentage of reticulocytes may appear increased compared to the overall number of RBCs. In order to get a more accurate assessment of bone marrow function, the calculated reticulocyte percentage (%) is often corrected with a calculation called a corrected reticulocyte count or a reticulocyte index (RI). This calculation compares the patient’s haematocrit with a normal haematocrit value. An additional calculation called the reticulocyte production index (RPI) is sometimes calculated to correct for the degree of reticulocyte immaturity – reflecting how quickly the reticulocytes were released from the bone marrow and how long it will take them to mature in the bloodstream. The RPI and maturation time vary with the haematocrit.

    Reticulocyte (%) = [Number of Reticulocytes / Number of Red Blood Cells] X 100

    Reticulocyte Index = Reticulocyte count (%) X [Measured haematocrit / Normal haematocrit]

    Reticulocyte Production Index = (Reticulocyte Index) X (1/maturation time)

    Some automated reticulocyte counts may have an immature reticulocyte fraction (IRF) and a mean reticulocyte volume (MRV) reported. They are primarily research parameters at this time. The reticulocyte count is a reflection of recent bone marrow activity. If your bone marrow is responding appropriately to the demand for increased numbers of RBCs, then the bone marrow will allow for the early release of more immature RBCs, increasing the number of reticulocytes in the blood.

    An increased reticulocyte percentage may indicate conditions such as:

    • Bleeding: If you bleed ((haemorrhage), then the number of reticulocytes will rise a few days later in an attempt to compensate for the red cell loss. If you have long-term (chronic) blood loss, then the number of reticulocytes will stay at an increased level as the marrow tries to keep up with the demand for new RBCs.
    • Haemolytic anaemia
    • Haemolytic disease of the newborn

    If your marrow is unable to keep up or is not functioning normally, then the number of reticulocytes may be normal or only slightly elevated despite demand but will eventually decrease due to lack of adequate production. If the number of reticulocytes is not elevated when you are anaemic, then it is likely that there is some degree of bone marrow disease or failure and/or a deficiency of erythropoietin. Decreased reticulocyte percentages may be seen, for example, with:

    The reticulocyte count gives an indication of what may be happening but cannot diagnose of any one particular disease. Reticulocyte count can show whether further investigations may be necessary and can help 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, then bone marrow RBC production is beginning to recover. In conditions causing RBC overproduction, the number of reticulocytes and RBCs, the concentration of haemoglobin, and percentage of haematocrit will all be increased.

  • Is there anything else I should know?

    Patients who move to higher altitudes may have increased reticulocyte counts as their body adapts to the lower oxygen content of their new location. Smokers also may demonstrate an increased number of RBCs and reticulocytes.

    Reticulocyte counts may be increased during pregnancy. Newborns have a higher percentage of reticulocytes, but the number drops to near adult levels within a few weeks.

    Traditionally, reticulocyte counts have been done manually by looking at a specially stained slide under the microscope and counting the number of reticulocytes in a number of fields of view. This method is still in use, but it is in the process of being replaced by automated methods that allow for a greater number of cells to be counted, thus enhancing the accuracy of reticulocyte counts.

  • Can the reticulocyte count be done on the same tube of blood as the RBC count or FBC?

    Yes. If anaemia is detected during a routine blood test, the doctor may request additional testing (including a reticulocyte count) on the same tube of blood, but it must be done on the same day, before the reticulocytes mature.

  • Will a blood transfusion affect reticulocyte results?

    Yes. Your doctor will decide how long you should wait after a transfusion before having a reticulocyte count performed.

  • How else might my doctor evaluate the cell production in my bone marrow?

    In some cases, a procedure called a bone marrow aspiration may be performed to obtain a sample of marrow to evaluate under the microscope. Sometimes this is the best way for a doctor to determine how well the bone marrow is functioning.

  • How long will it take to get results of a reticulocyte count result?

    Most laboratories provide a reticulocyte count result t within 24 hours of sample collection.