The Immature Reticulocyte Fraction (IRF) in the Sysmex XN-1000V Analyzer Can Differentiate between Causes of Regenerative and Non-Regenerative Anemia in Dogs and Cats

Simple Summary Anemia is a frequent problem in small animals with several underlying causes, each one with different treatments and prognosis. When facing a sick patient, veterinary clinicians need to correctly identify the problem behind this pathology as soon as possible. Some hematology analyzers provide a new parameter (the immature reticulocyte fraction, IRF) which has been used in human medicine for this purpose. Our results show that IRF is also able to differentiate between some causes of anemia. This new parameter may help veterinary clinicians to further advance in their diagnosis and focus on more specific tests for their patients.Abstract The Sysmex XN-1000V analyzer can identify those reticulocytes with high RNA content and fluorescence, providing the immature reticulocyte fraction (IRF). While this parameter has been used in human medicine to identify the cause of anemia, few studies have focused on its use in veterinary medicine. In this study, we determined the IRF and related reticulocyte parameters in a large population of non-anemic and anemic dogs and cats (subclassified depending on the origin of their anemia). The IRF was significantly higher in hemolytic anemias compared to hemorrhagic ones in both species. Moreover, the IRF was significantly lower in dogs and cats with bone marrow failure than in other non-regenerative anemias and in both groups compared to pre-regenerative anemias. The accurate cut-off values for the differential in regenerative anemias and reference ranges for both species using the Sysmex XN-1000V are also reported. The measurement of the IRF in this analyzer can help clinicians to further classify the type of anemia in both species.