Reticulocytes are immature RBCs. As RBC precur-
sors mature (Fig. 1–2), the cell nucleus decreases in
size and eventually becomes a dense, structureless
9 CHAPTER 1—Hematology and Tests of Hematopoietic Function
01CAVA chp-01 3/7/03 10:58 AM Page 9mass.
At the same time, the hemoglobin content of
the cell increases. Reticulocytes are cells that have
lost their nuclei but still retain fragments of mito-
chondria and other organelles. They also are slightly
larger than mature RBCs.
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.
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 (more info about hemoglobin formation can be found here:
hemoglobin formation)
After blood loss or effec-
tive 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 reticulo-
cyte count (reticulocytopenia) because the cells
never mature sufficiently to enter the peripheral
circulation.
Performing a reticulocyte count involves examin-
ing a stained smear of peripheral blood to determine
the percentage of reticulocytes in relation to the number of RBCs present.
