Only aggregate reticulocytes are counted in cats.
Retics can be punctate (mature, single dot) or aggregate (immature, strand), based on how the RNA stains.
This is relevant in cats, in which punctate retics can persist in circulation for seven-ten days.
Therefore, in cats, only count aggregate retics to accurately interpret regenerative status.
In other species, both types can be counted because they have similar half-lives.
In dogs and cats, increased reticulocytes indicate a regenerative anemia, in which the bone marrow is responding to a need for more red blood cells (RBC) by releasing immature RBCs.
When you stain blood with new methylene blue (NMB), the immature, polychromatophilic RBCs that contain RNA show up under the microscope as “reticulocytes.”
Normal RBCs show up yellowish with NMB stain, but immature RBCs show up with bluish dots or clumps inside (that’s the RNA).
Immature RBCs are polychromatophilic (usually they stain a darker blue than normal RBCs) on routine Romanowsky-based polychrome stains (e.g., Wright’s, DiffQuik).
Increased polychromasia SUGGESTS a regenerative anemia, but you need a reticulocyte count to confirm it.
Reticulocyte counts are usually expressed as the # of retics per 1000 RBCs.
