Neutrophil counts and morphology in Cats: A retrospective case-control study of 517 cases

Neutrophil count and morphological abnormalities are common in ill cats. This retrospective study examined the associations between these parameters and clinical and clinicopathologic findings, morbidity, mortality and the final diagnoses in a large population of ill cats, in a teaching hospital setting. The study included 517 cats, divided into three groups based on their neutrophil count; neutropenia (26 cats, 5%), within reference interval (WRI, 313 cats, 61%) and neutrophilia (178 cats, 34%). Occurrence of neutrophilic left shift and cytoplasmic toxicity was recorded. There were significant (P<0.05) group differences in concentrations of albumin, total protein, globulin, urea and bilirubin, aspartate aminotransferase and creatine kinase activities, and in frequencies of sepsis (P<0.0001), high rise syndrome (P=0.014), acute kidney injury (P=0.01), peritonitis (P=0.001), chronic kidney disease (P=0.023), pleural effusion (P=0.0002), pyothorax (P=0.012) and feline immunodeficiency virus (FIV) infection (P=0.02). The frequency of neutrophilia was unexpectedly high in FIV-infected cats (17/29, 59%). Neutrophil cytoplasmic toxicity and left shift occurred in 57% and 10% of the cats, respectively. Both were significantly more frequent in cats with neutrophilia or neutropenia compared to the group with neutrophil count WRI (P<0.0001). Mortality rate was higher (P<0.0001) in cats with neutropenia or neutrophilia. The area under the receiver operating characteristic curve of the neutrophil count as a predictor of mortality was 0.61 (95% confidence interval 0.55-0.68). Cost of treatment and hospitalization duration significantly differed between groups. Presence of left shift was significantly associated with mortality (P=0.004). Concurrent neutropenia or neutrophilia with cytoplasmic toxicity and left shift was significantly associated with mortality.