Manual reticulocyte counts

Assessment of regeneration is the very first step in the evaluation of anemia to determine if the anemia is regenerative or non-regenerative in dogs and cats. We do not routinely use manual reticulocyte counts in other species such as equids, small ruminants, camelids, or bovids because they either do not release immature RBC’s into circulation when anemic or they do so inconsistently. Specific causes of regenerative and non-regenerative anemia will be discussed in your Clinical Pathology Course (Hematology), but in this laboratory, we will practice how to assess erythrocyte regeneration in our patients using new methylene blue stain.

In both normal cell turnover and anemia, immature erythrocytes are released into circulation.  Reticulocytes are immature, non-nucleated RBCs that contain RNA and continue to synthesize hemoglobin even after they lose the nucleus (metarubricyte stage). The term “reticulocyte” is synonymous with the term “polychromatophil” observed on Romanowsky stain (Diff Quik, Wright Giemsa, etc.) and many of our benchtop hematology analyzers will provide either a reticulocyte percentage or a reticulocyte count. In cases in which you suspect regeneration and your analyzer does not provide a reticulocyte count or you suspect a concurrent Heinz body anemia, we use New Methylene Blue (NMB) stain to perform a manual reticulocyte count. Heinz bodies also stain with NMB stain.

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