Retrospective investigation of the neutrophil-to-lymphocyte ratio in dogs with pneumonia: 49 cases (2011–2016)

Abstract

Objective: To assess the utility of the neutrophil-to-lymphocyte ratio (NLR) in predicting outcome in canine pneumonia compared with routine hematological parameters and systemic inflammatory response syndrome (SIRS) scores. Design: Retrospective study. Setting: University teaching hospital. Animals: Forty-nine client-owned dogs. Interventions: None. Measurements and Main Results: Medical records were reviewed to identify dogs with a diagnosis of pneumonia from July 2011 to December 2016. Signalment, clinical findings, laboratory characteristics, and outcome were recorded. Inclusion criteria were a clinical and radiographic diagnosis of pneumonia, plus reference laboratory hematology at diagnosis. Cases that received steroids were excluded. Euthanized dogs were only included in statistical analysis if euthanized solely due to pneumonia severity. The NLR, total WBC count, neutrophil count, lymphocyte count, band neutrophil percent of total WBC count (%-bands), and percentage of cases diagnosed with SIRS were compared between survivors and nonsurvivors. Receiver operating characteristic curves were generated to identify optimal sensitivity and specificity cutoffs for nonsurvival to discharge. Two hundred records were retrieved; 49 cases fulfilled the inclusion criteria. Of these, 33 (67%) survived to discharge. The NLR did not differ significantly between the survivors and nonsurvivors, nor did total WBC count or neutrophil count. Survivors had a significantly lower %-bands than nonsurvivors (P < 0.001) and higher lymphocyte count (P = 0.004). The mortality rate did not differ significantly between dogs with and without SIRS. Receiver operating characteristic analysis identified a %-bands cutoff of 2.5% or higher had an 83% sensitivity and 79% specificity for nonsurvival. Conclusions: Unlike in human medicine, neither NLR nor SIRS scores predicted outcome in this cohort of dogs with pneumonia. However, survivors had a lower %-bands and higher lymphocyte count than nonsurvivors, which may be helpful prognostically in clinical cases.