Etiology and outcome of extreme neutrophilic leukocytosis: A multi‐institutional retrospective study of 269 dogs

BACKGROUND: The magnitude of diagnostic abnormalities can influence the perception of clinical outcome. Extreme neutrophilic leukocytosis (ENL) is an uncommon finding caused by markedly increased granulopoiesis. A lack of recent, large‐scale studies limits our understanding of the importance, causation, and prognosis associated with ENL in dogs. HYPOTHESIS/OBJECTIVES: Describe disease categories (DC) identified in dogs with ENL and identify variables associated with survival. We hypothesized that factors including fever, segmented and band neutrophil counts, and DC would be negatively associated with survival. ANIMALS: Two‐hundred sixty‐nine dogs with ENL (segmented neutrophils ≥50 × 10(3) cells/μL) presented to the veterinary teaching hospitals at Auburn University (n = 164), the University of Missouri (n = 81), and Oklahoma State University (n = 24) between January 1, 2009 and December 31, 2019. METHODS: Retrospective study. Demographic data and outcome variables including temperature, CBC findings, DC, duration of hospitalization (DOH) and outcome were acquired from the medical record. Statistical analyses included chi‐squared and Kruskal‐Wallis tests, and Pearson product moment correlations with a P < .05 significance level. RESULTS: Mortality was 41%. Survival differed with DC (P = .002). Mortality was higher (P < .05) in dogs with neoplasia (56.2%) vs immune‐mediated disease (20.5%) or tissue damage/necrosis (19%). Weight (P = .001, r = −0.14) and total neutrophil count (P = .04, r = −0.02) were weakly negatively associated with survival whereas DOH was weakly positively associated with survival (P = .03, r = 0.14). CONCLUSIONS AND CLINICAL IMPORTANCE: Mortality in dogs with ENL is high but differed according to DC. Only weak correlations between clinical or clinicopathologic variables and mortality were identified. Extreme neutrophilic leukocytosis should be interpreted in conjunction with the underlying disease process, and not broadly used to predict clinical outcome.