Diagnostic and prognostic significance of rubricytosis in dogs: A retrospective case-control study of 380 cases

Peripheral nucleated red blood cells (pnRBC, rubricytosis) are observed in dogs in various disorders. In humans, pnRBC are associated with high morbidity and poor prognosis. This retrospective case-control study aimed to characterize the laboratory findings, diagnoses and prognoses of dogs with rubricytosis. Data from the medical records of 380 dogs with rubricytosis and 356 negative controls were compared using appropriate statistical methods. Dogs with pnRBC were older compared to controls (median age 7.3 years vs. 5. 7 years; P<0.001), had higher (P<0.05) counts of leukocytes, segmented and band neutrophils and lower hematocrit, hemoglobin concentration, red blood cell count, mean corpuscular volume, mean corpuscular hemoglobin concentration, and more serum chemistry abnormalities compared to controls. They had higher (P<0.035) occurrence of heatstroke, immune mediated hemolytic anemia (IMHA), lymphoma, hemangiosarcoma, anticoagulant poisoning, bite wounds and mast cell tumors compared to controls. Dogs with pnRBC had a higher mortality rate (P=0.001) compared to controls, and it significantly increased with the absolute pnRBC count. The mortality rate significantly (P<0.0001) increased with an increase in the absolute nRBC count quartile. However, the absolute pnRBC count was an inaccurate outcome predictor (area under the receiver operator characteristics curve, 0.62). Rubricytosis in dogs is associated with multiple hematological and serum chemistry abnormalities and higher mortality. Most rubricytosis-associated hematological abnormalities were due to regenerative anemia, likely because IMHA and blood loss were significantly more common in the rubricytosis group. In dogs, as in humans, presence of pnRBC was a negative prognostic indicator.