Comparison of manual polychromatophilic cell and automated reticulocyte quantification in evaluating regenerative response in anemic dogs

Background Degree of polychromasia and reticulocyte counts are commonly used in veterinary medicine to evaluate response to anemia. The quantitative association between these 2 measurements has not been evaluated. Objective The aim of this retrospective study was to compare automated reticulocyte percents and counts with those of polychromatophilic cells on blood films from dogs. Methods Blood films and medical records from 30 clinically healthy dogs and 60 anemic dogs were evaluated. Manual percentage of polychromatophilic cells (MPP) was determined by counting cells in 10 1000x fields, and automated reticulocyte percentage (ARP) was measured using an ADVIA 120 hematology analyzer; absolute polychromatophilic cell and reticulocyte counts were then calculated. Degree of polychromasia, estimated as slight, mild, moderate, marked was documented. Percentages and absolute counts of polychromatophilic cells and reticulocytes were compared using least squares regression and Pearson's correlation coefficients. Results The reference interval for MPP in healthy dogs was 0.210.26%. Correlation between MPP and ARP was highest when all levels were considered (n=60, r=.98, P<.0001), strong when ARP was>5% (n=20, r=.91, P<.0001), and poor when ARP was 12% (n=20, r=.35, P<.0001). Results were similar for comparisons of absolute reticulocyte and polychromatophilic cell counts, with the best correlation found when all levels of counts were analyzed together (r=.96) and for automated reticulocyte counts>150,000/mu L (r=.94). Correlation of estimates of polychromasia with ARP was good (r=.83). Conclusion In anemic dogs MPP can be used for assessment of regeneration, especially in dogs with higher levels of ARP. Standard quantification of reticulocytes is more accurate in dogs with lesser degrees of regeneration.