There are two types of RNA-containing red cells in cat blood. The aggregate reticulocytes are red cells with clumps of blue-stained granules and the punctate reticulocytes are red cells with fewer, smaller blue granules. The aggregate reticulocytes mature into punctate reticulocytes within 12-24 hours; punctate reticulocyte circulate for at least several days (7-10 days) before all the RNA is lost. The reticulocyte count in cat blood should only include the percentage of aggregate reticulocytes; punctate reticulocytes are not counted as they do not reflect the most recent bone marrow response (e.g. an anemic cat with only punctate reticulocytes is not actively regenerating at this time, but has shown some bone marrow regeneration in the past 7-10 days).
At normal hematocrits, few reticulocytes are released at the aggregate stage. Non-anemic cats have only 0 to 1% aggregate reticulocytes but may have as high as 10% punctate reticulocytes. With moderate to severe anemia due to blood loss or hemolytic disease, the healthy cat marrow increases the rate of erythropoiesis and releases aggregate reticulocytes, thereby raising the reticulocyte count. Since only aggregate reticulocytes are included in the count, the result is a fairly good indicator of the degree of the present marrow regenerative response. Note that in mild anemias, cats may only release punctate reticulocytes.
The following table is a guide to the expected reticulocyte counts for cats with regenerative response to anemia:
|Degree of Regeneration||Reticulocyte %||Absolute aggregate reticulocytes (/uL)|
|Marked||≥ 5.0||≥ 200,000|
* These values are dependent on the upper limit of the reference interval for reticulocytes (% and absolute) that is established in the laboratory and may change over time (when new intervals are created).
Remember that punctate reticulocytes are larger than normal red blood cells (macrocytic) but do not stain as polychromatophils in a Wright's stained blood smear (they are normochromic). Punctate reticulocytes can persist in the circulation for up to 21 days and are often responsible for a post-regenerative macrocytosis in cats (i.e. the cat is macrocytic but no longer anemic). Normochromic macrocytes may also be seen in the blood of cats with poorly regenerative anemia due to myelodysplasia or acute myeloid leukemia, where they are a reflection of abnormal dysplastic ("megaloblastoid") differentiation.