Reticulocytes are immature RBCs. As RBC precursors mature (Fig. 1-2), the cell nucleus decreases in size and eventually becomes a dense, structureless mass.¹⁰ At the same time, the hemoglobin content of the cell increases. Reticulocytes are cells that have lost their nuclei but still retain fragments of mitochondria and other organelles. They also are slightly larger than mature RBCs.¹¹ RBCs normally enter the circulation as reticulocytes and attain the mature form (erythrocytes) in 1 to 2 days.

Under the stress of anemia or hypoxia, an increased output of erythropoietin may lead to an increased number of circulating reticulocytes (see Table 1-1). The extent of such an increase depends on the functional integrity of the bone marrow, the severity and duration of anemia or hypoxia, the adequacy of the erythropoietin response, and the amount of available iron.¹² For example, a normal reticulocyte count in the presence of a normal hemoglobin level indicates normal marrow activity, whereas a normal reticulocyte count in the presence of a low hemoglobin level indicates an inadequate response to anemia. This may be a result of defective erythropoietin production, bone marrow function, or hemoglobin formation. After blood loss or effective therapy for certain kinds of anemia, an elevated reticulocyte count (reticulocytosis) indicates that the bone marrow is normally responsive and is attempting to replace cells lost or destroyed. Individuals with defects of RBC maturation and hemoglobin production may show a low reticulocyte count (reticulocytopenia) because the cells never mature sufficiently to enter the peripheral circulation.

Performing a reticulocyte count involves examining a stained smear of peripheral blood to determine the percentage of reticulocytes in relation to the number of RBCs present.

• Evaluation of the adequacy of bone marrow response to stressors such as anemia or hypoxia:
  • A normal response is indicated by an increase in the reticulocyte count.
  • Failure of the reticulocyte count to increase may indicate depressed bone marrow functioning, defective erythropoietin production, or defective hemoglobin production.
• Evaluation of anemia of unknown etiology to determine the type of anemia:
  • Elevated reticulocyte counts are found in hemolytic anemias and sickle cell disease.
  • Decreased counts are seen in pernicious anemia, thalassemia, aplastic anemia, and severe iron-deficiency anemia.
• Monitoring response to therapy for anemia:
  • In iron-deficiency anemia, therapeutic administration of iron should produce reticulocytosis within 3 days and the count should remain elevated until normal hemoglobin levels are achieved.
  • Vitamin B₁₂ therapy for pernicious anemia should cause a prompt, continuing reticulocytosis.
• Monitoring physiologic response to blood loss:
  • After a single hemorrhagic episode, reticulocytosis should begin within 24 to 48 hours and peak in 4 to 7 days.
  • Persistent reticulocytosis or a second rise in the count indicates continuing blood loss.
• Confirmation of aplastic crisis in clients with known aplastic anemia as evidenced by a drop in the usually high level of reticulocytes, indicating that RBC production has stopped despite continuing RBC destruction¹³

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

If the client is an adult, a venipuncture is performed and the sample is collected in a lavender-topped tube. A capillary sample may be obtained in infants and children as well as in adults for whom venipuncture may not be feasible.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample (see Appendix I).

• Abnormal values: Note and report fatigue, weakness, and color changes associated with a decrease in counts and pain, and changes in mental state and visual perception associated with an increase in counts. Increased counts in 4 to 7 days indicate that the therapy to treat loss of RBCs is effective, whereas decreased counts indicate an ineffective production of RBCs, and further testing and evaluation are needed to determine the cause. Assess for continuing blood loss (pulse, blood pressure, skin color, weakness, dizziness).
• Critical values: Polycythemia with reticulocyte increases of greater than 20 percent requires immediate communication to the physician. Prepare the client for possible phlebotomy to reduce volume of blood and intravenous fluids to reduce viscosity of blood. Administer ordered myelosuppressive drugs.