Reticulocyte
A reticulocyte is an immature erythrocyte (i.e., red blood cell), which are primarily present in bone marrow but may circulate in blood. When reticulocytes circulate in a higher than normal percentage of erythrocytes, it suggests that erythropoiesis is being hyperactive. When the reticulocyte percentage is zero to low in the presence of anemia, it suggests depressed erthryopoiesis.
The name comes from a microscopic staining technique by which they were first characterized, in which parts of the ribosomes collect in a "reticulated" pattern. This collection is not the same as the endoplastic reticulum.
Role in erythropoiesis
In erythropoeisis, reticulocytes are the successor to nucleated erythrocytes. While they have no nucleus, they still contain RNA. In excess of 90% of their protein content is hemoglobin, and up to 30% of the total hemoglobin in adult erythrocytes is created at the reticulocyte stage. [1]
Corrections for clinical utility
While the basic laboratory report on reticulocytes is their percentage relative to all erythrocytes, this measurement alone is misleading. It must be corrected both for the absolute number of erythrocytes including reticulocytes, [2]
Absolute Reticulocyte Count = # or % retics * (Pt's Hct / Normal Hct)
and for the effect of erythropoetin released in anemia.
Reticulocyte Index = Absolute Retic Ct / Maturation FactorReticulocyte maturation factors
| Hematocrit (Hct) | Reticulocyte maturation factor |
|---|---|
| Hct ≥ 45% | 1.0 |
| 45% > Hct ≥ 35% | 1.5 |
| 25% > Hct ≥ 15% | 2.0 |
| 15% ≠> Hct | 2.5 |
In the presence of decreases in erythrocytes,
- Normal patients will respond to a Hct < 30% with a 2 to 3 increase in maturation factor
- Patients with severe hemolytic anemia can show 6-fold increase
- When bone marrow disease or deficiency of erythrocyte precursors are present, the maturation factor is less than 2
References
- ↑ Frazier JF et al. (April 1982), "Studies of the Transferrin Receptor on both Human Reticulocytes and Nucleated Human Cells in Culture: Comparison of factors regulating receptor density", J. Clin. Invest. 69: 853-865
- ↑ Fauci AS, et al. (14th Edition, 1998), Harrison's Principles of Internal Medicine, McGraw-Hill, ISBN 0070202915, p. 337}}