A reticulocyte—a young, immature, nonnucleated RBC—contains reticular material (RNA) that stains gray-blue. Reticulum is present in newly released blood cells for 1–2 days before the cell reaches its full mature state. Normally, a small number of these cells are found in circulating blood. For the reticulocyte count to be meaningful, it must be viewed in relation to the total number of erythrocytes (absolute reticulocyte count = % reticulocytes × erythrocyte count).

The reticulocyte count is used to differentiate anemias caused by bone marrow failure from those caused by hemorrhage or hemolysis (destruction of RBCs), to check the effectiveness of treatment in pernicious anemia and folate and iron deficiency, to assess the recovery of bone marrow function in aplastic anemia, and to determine the effects of radioactive substances on exposed workers.

Adults: 0.5%–1.5% of total erythrocytes (women may be slightly higher)

Newborns: 3%–6% of total erythrocytes (drops to adult levels in 1–2 months)

Absolute count: 25–85 × 10³/mm³ or × 10⁹ cells/L

Reticulocyte index (RI): 1% corrected reticulocyte count

Hct correction for anemia: RI = reticulocyte count × (patient’s Hct/45)

1. Obtain 5 mL of whole blood in a lavender-topped tube (with EDTA). Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

2. Mix the blood sample with a supravital stain such as brilliant cresyl blue. Allow the stain to react with the blood, prepare a smear with this mixture, and scan under a microscope. Count and calculate the reticulocytes.

1. Increased reticulocyte count (reticulocytosis) means that increased RBC production is occurring as the bone marrow replaces cells lost or prematurely destroyed. Identification of reticulocytosis may lead to the recognition of an otherwise occult disease, such as hidden chronic hemorrhage or unrecognized hemolysis (e.g., sickle cell anemia, thalassemia). Increased levels are observed in the following:

   1. Hemolytic anemia

      1. Immune hemolytic anemia

      2. Primary RBC membrane problems

      3. Hemoglobinopathic and sickle cell disease

      4. RBC enzyme deficits

      5. Malaria

   2. After hemorrhage (3–4 days)

   3. After treatment of anemias

      1. An increased reticulocyte count may be used as an index of the effectiveness of treatment.

      2. After adequate doses of iron in iron-deficiency anemia, the rise in reticulocytes may exceed 20%.

      3. There is a proportional increase when pernicious anemia is treated by transfusion or VB₁₂ therapy.

2. Decreased reticulocyte count means that bone marrow is not producing enough erythrocytes; this occurs in:

   1. Untreated iron-deficiency anemia

   2. Aplastic anemia (a persistent deficiency of reticulocytes suggests a poor prognosis)

   3. Untreated pernicious anemia

   4. Anemia of chronic disease

   5. Radiation therapy

   6. Endocrine problems

   7. Bone marrow failure (infection or cancer)

   8. Myelodysplastic syndromes

   9. Alcoholism

3. RI implications:

   1. <2% indicates hypoproliferative component to anemia

   2. >2%–3% indicates increased RBC production

Pretest Patient Care

1. Explain test purpose and procedure. Pretest and posttest care are the same as for the hemogram. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

2. Note medications. Some drugs cause aplastic anemia.