Toxic neutrophils in cats: clinical and clinicopathologic features, and disease prevalence and outcome--a retrospective case control study

Toxic neutrophils exhibit a variety of nuclear and cytoplasmic abnormalities in Romanowsky-stained blood smears, and are associated with inflammation and infection. The purpose of the retrospective study reported here was to investigate the association of toxic neutrophils with clinicopathologic characteristics, diseases, and prognosis in cats. Cats with toxic neutrophils (n = 150) were compared with negative-control cats (n = 150). Statistical analyses included Fisher exact, independent t-, nonparametric Mann-Whitney, and chi-squared tests. Cats with toxic neutrophils had significantly (P < .05) higher prevalence of fever, icterus, vomiting, diarrhea, depression, dehydration, weakness, and cachexia, as well as leukocytosis, neutrophilia, left shift, neutropenia, anemia, hypokalemia, and hypocalcemia. The prevalence of shock, sepsis, panleukopenia, peritonitis, pneumonia, and upper respiratory tract diseases was significantly higher among these cats, as were infectious (viral and bacterial) and metabolic disorders. Control cats had a significantly higher prevalence of feline asthma, as well as allergic, idiopathic, and vascular disorders. Hospitalization duration and treatment cost were significantly (P < .001) higher in cats with toxic neutrophils. In 53 and 47% of the cats with toxic neutrophils, the leukocyte and neutrophil counts were normal, respectively, whereas in 43%, both abnormalities and left shift were absent, and toxic neutrophils were the only hematologic evidence of inflammation or infection. In conclusion, toxic neutrophils were found to be associated with certain clinicopathologic abnormalities, and when present, may aid in the diagnosis, as well as the assessment of hospitalization duration and cost. The evaluation of blood smears for toxic neutrophils provided useful clinical information.