Spurious reticulocyte profiles in dogs with large form babesiosis: a retrospective study

Erroneously high reticulocyte counts (pseudoreticulocytosis) have been reported in dogs with leukemia. Pseudoreticulocytosis and an abnormal reticulocyte profile were observed in a dog with large form babesiosis presented at our institution.

The aims of this retrospective study were to determine if dogs with babesiosis and other dogs had abnormal reticulocyte profiles, and to correlate these profiles with the primary diagnosis.

All canine CBCs obtained with the Sysmex XT-2000iV or Procyte DX were reviewed. Cases of large form babesiosis were identified and their reticulocyte dot plots were analyzed. Dogs with abnormal reticulocyte profiles but without microscopically apparent intraerythrocytic Babesia piroplasms were identified. The reticulocyte profiles and fluorescence ratios of dogs with and without babesiosis were compared.

Twenty of 92 dogs with babesiosis had abnormal reticulocyte profiles, including 8 with a separation between the reticulocyte and mature RBC plots or a continuum of reticulocytes from the RBC plot but with a higher density of dots in the middle of the "comet tail" than in the left quarter of the dot plot. Thirteen of 6980 dogs without Babesia on the blood smear had abnormal reticulocyte profiles, including 3 with leukemia. The medium-fluorescence reticulocyte ratios tended to be higher in dogs with babesiosis and abnormal dot plots than in other dogs, whereas the high-fluorescence ratio was higher in one dog with leukemia.

Abnormal reticulocyte dot plots and atypical reticulocyte fluorescence ratios may occur in dogs with babesiosis and alert clinical pathologists to consider this diagnosis.