Background
A reticulocyte-a young, immature, nonnucleated red blood cell (RBC)-contains reticular material (RNA) that stains gray-blue. Reticulum is present in newly released blood cells for 1 to 2 days before the cells reach their fully 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 x erythrocyte count).
The reticulocyte count is used to differentiate anemias caused by bone marrow failure from those caused by acute or chronic blood loss or hemolysis (destruction of RBCs); assess the effectiveness of treatment in pernicious anemia and folate and iron deficiency anemias; assess the recovery of bone marrow function in aplastic anemia; and determine the effects of radioactive substances on exposed workers.
Normal reference values
Adults: 0.5% to 1.5% of total erythrocytes (percentage may be slightly higher in women)
Absolute count: 25,000 to 75,000/mcL1
Reticulocyte production index (RPI) = [% reticulocyte count x patient hematocrit (Hct)]/45(normal Hct)2
Clinical implications
An 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 (for example, sickle cell anemia, or thalassemia). Reticulocytosis is observed in the following:
* hemolytic anemia
* immune hemolytic anemia
* primary RBC membrane problems
* hemoglobinopathic and sickle cell disease
* RBC enzyme deficits
* after hemorrhage (3 to 4 days)
* after treatment of anemias.
An increased reticulocyte count may be used as an index of treatment effectiveness. After adequate doses of iron in iron-deficiency anemia, the rise in reticulocytes may exceed 20%. There is a proportional increase when pernicious anemia is treated by transfusion or vitamin B12 therapy.
A decreased reticulocyte count (reticulocytopenia) means that the bone marrow is not producing enough erythrocytes. This occurs in:
* untreated iron-deficiency anemia
* aplastic anemia (a persistent deficiency of reticulocytes suggests a poor prognosis)
* untreated pernicious anemia
* anemia of chronic disease
* radiation therapy
* endocrine disorders
* tumor in bone marrow (bone marrow failure)
* myelodysplastic syndromes
* alcoholism.
Source: Fischbach FT, Fischbach MA. A Manual of Laboratory and Diagnostic Tests. 10th ed. Philadelphia, PA: Wolters Kluwer; 2018.
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