EBM Consult

Lab Test: Reticulocyte Count

    Lab Test
    • Reticulocyte Count
    • Measurement of percentage of reticulocytes in peripheral blood for evaluation of erythropoietic activity and to help direct clinical management of anemia
    Reference Range
    • Adults:  0.5%-2.5% of total erythrocytes (RBCs)
    • Infants:  0.5%-7% of total erythrocytes (0.03-0.07 erythrocytes)
    • Reticulocyte Index:  1.0
    Indications & Uses
    • Differentiation between hyporegenerative and hyperregenerative states in unexplained anemia.
    • Decreased reticulocyte count: 
      • Reticulocytopenia (diminished number of reticulocytes) occurs in patients with marrow ablative disorders, impaired erythropoiesis, or decreased endogenous erythropoietin. 
    • Anemias associated with suppressed bone marrow function include aplastic anemia, aplastic crisis in sickle cell disease, pernicious anemia pure red cell aplasia, thalassemic syndromes, and transient neonatal erythroblastopenia. 
    • Anemias associated with bone narrow ablative/infiltration disorders include acute leukemia, lymphoma myelodysplastic syndromes, myelofibrosis, myeloma, and metastatic carcinoma.
    • Reticulocytosis:
      • The erythropoietic activity of the bone marrow and the rate of cell delivery into the peripheral circulation determine the number of reticulocytes in the peripheral blood. 
      • Reticulocytosis (an increased number of peripheral blood reticulocytes) may be seen with anemia in the presence of functional bone marrow (e.g., blood loss, intravascular hemolysis, polycythemia vera, exogenous erythropoietin administration, or replacement of folate or iron).
      • In patients with sickle cell disease, the average steady-state reticulocyte count is 12% (range of 5% to 30%; normal adult range:  0.5% to 2.5% cells).
      • In children having a positive sickle cell screen in the emergent setting, a high reticulocyte count alone (above 2% cells) was more sensitive in differentiating sickle cell disease from sickle cell trait.  
      • Should be considered in all men unless there is another obvious cause of priapism.
    Clinical Application
    • The reticulocyte count is a test for determining bone marrow function and evaluating erythropoietic activity. 
    • This test is also useful in classifying anemias. 
    • A reticulocyte is an immature red blood cell (RBC) that can be readily identified under a microscope by staining the peripheral blood smear with Wright or Giemsa stain.  It is an RBC that still has some microsomal and ribosomal material left in the cytoplasm.  It sometimes takes a few days for that material to be cleared from the cell.  Normally there are a small number of reticulocytes in the bloodstream. 
    • The reticulocyte count gives an indication of RBC production by the bone marrow.  Because the reticulocyte count is a percentage of the total number of RBCs, a normal to low number of reticulocytes can appear high in the anemic patient, because the total number of mature RBCs is low.  The reticulocyte index in a patient with a good marrow response to the anemia should be 1.0.  If it is below 1.0, even though the reticulocyte count is elevated, the b one marrow response is inadequate in its ability to compensate (as see in iron deficiency, vitamin B12 deficiency, marrow failure). 
    • Increased levels may indicate:
      • Hemolytic anemia (e.g., immune hemolytic anemia, hemoglobinopathies, hypersplenism, trauma from a prosthetic heart valve), hemorrhage (3 to 4 days later), hemolytic disease of the newborn, or treatment for iron, vitamin B12, or folate deficiency
    • Decreased levels may indicate:
      • Pernicious anemia and folic acid deficiency, iron-deficiency anemia, aplastic anemia, radiation therapy, malignancy, marrow failure, adrenocortical hypofunction, anterior pituitary hypofunction, or chronic diseases.  Results increased in high-altitude residence. Results decreased in chronic renal disease.
    Related Tests
    • Anemia panel
    • Hemolysis panel
    • Hemoglobin and hematocrit - indirect measurements of the RBCs
    • Red blood cell count - direct count of the total number of RBCs
    Drug-Lab Interactions
    • Pregnancy may cause an increased reticulocyte count.
    • Howell-Jolly bodies are blue stippling material in the RBC that occurs in severe anemia or hemolytic anemia.  The RBCs containing these Howell-Jolly bodies look like reticulocytes and can be miscounted by some automated counter machines as reticulocytes; this give s a falsely high number of reticulocytes.
    Test Tube Needed
    • Whole blood in EDTA (lavender top) tube
    • Collect 5 mL of whole blood or capillary blood with direct dilution. 
    • Apply pressure or a pressure dressing to the venipuncture site and assess the site for bleeding.
    Storage and Handling
    • Perform test within 6 hours at room temperature, or store up to 72 hours at 2° to 6°C.
    What To Tell Patient Before & After
    • Explain the procedure to the patient.
    • Tell the patient that no fasting is required.
    • Brugnara C.  Reticulocyte cellular indices: a new approach in the diagnosis of anemias and monitoring of erythropoietic function. Crit Rev Clin Lab Sci 2000;37(2):93-130.
    • Piva E et al. Automated reticulocyte counting: state of the art and clinical applications in the evaluation of erythropoiesis.  Clin Chem Lab Med 2010;48(10):1369-1380.
    • LaGow B et al., eds. PDR Lab Advisor. A Comprehensive Point-of-Care Guide for Over 600 Lab Tests.  First ed. Montvale, NJ: Thomson PDR; 2007.
    • Pagana K, Pagana TJ eds. Mosby's Manual of Diagnostic and Laboratory Tests. 5th Ed.  St. Louis, Missouri. 2014.

MESH Terms & Keywords

  • Reticulocyte Count