Peripheral nucleated red blood cells in cats and their association with age, laboratory findings, diseases, morbidity and mortality – a retrospective case-control study

Metarubricytosis occurs in cats in various disorders. This retrospective case-control study characterized the clinical and laboratory findings, diagnoses and prognoses of 117 cats presenting metarubricytosis, compared to 201 negative, time-matched controls. Cats with metarubricytosis were younger (P = 0.043) compared to the controls (median 3.5 years; range 0.1-19.0 vs. median 6.0 years; range 0.1-21.0, respectively). They had higher (P < 0.03) frequency of weakness, depression, dyspnea, hypothermia, shock, epistaxis and anemia compared to the controls, and presented higher (P < 0.05) median leukocyte count and mean corpuscular volume, lower (P < 0.001) hematocrit, hemoglobin concentration, RBC count and mean corpuscular hemoglobin concentration compared to the controls. Cats with metarubricytosis had higher (P < 0.01) serum muscle enzyme activities and hyperbilirubinemia, and lower (P = 0.01) total protein concentration compared to the controls. They had higher (P = 0.01) frequencies of traumatic disorders (i.e., hit by car, high rise syndrome, fractures, pneumothorax and lung contusions), pyothorax and hemoplasmosis-associated hemolytic anemia compared to the controls. Cats with metarubricytosis showed a higher (P = 0.05) mortality rate, longer hospitalization and higher treatment cost compared to the controls. Nevertheless, the absolute peripheral nucleated red blood cell count was an inaccurate outcome predictor. Metarubricytosis in cats is associated with anemia, multiple hematological and serum biochemistry abnormalities and higher morbidity and mortality. Most metarubricytosis-associated hematological abnormalities were attributed to regenerative anemia (i.e., physiologic metarubricytosis), hemolysis, and trauma. The latter likely led to metarubricytosis due to shock, inflammation and hypoxia. In cats, according to our assessment, metarubricytosis should be considered a negative prognostic indicator, warranting intensive treatment and monitoring.