Neutrophil-to-lymphocyte ratio is increased in dogs with acute congestive heart failure secondary to myxomatous mitral valve disease compared to both dogs with heart murmurs and healthy controls.

Objective: To retrospectively evaluate neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) as a biomarker for severity and short-term outcomes of congestive heart failure (CHF) secondary to myxomatous mitral valve disease (MMVD) in dogs.

Animals: 47 dogs with CHF secondary to MMVD, 47 dogs with presumptive preclinical MMVD, and 47 control dogs.

Methods: Medical record data (signalment, physical examination findings, medical treatments instituted, American College of Veterinary Internal Medicine MMVD stage, length of hospitalization, outcome, and hospital re-presentation due to CHF) from March 2012 through March 2022 for each dog were collected. Statistical analyses were performed with Mann-Whitney, Spearman correlation, and Fisher exact tests.

Results: NLR (but not PLR) was significantly higher in dogs with CHF secondary to MMVD (6.41) compared to presumptive preclinical MMVD dogs (4.66; P < .001) and control dogs (3.95; P < .001). Dogs with higher NLR and PLR received significantly higher cumulative dosages of loop-diuretic therapy during hospitalization (ρ = 0.3, P = .04; and ρ = 0.4, P = .02, respectively). There was a positive association between NLR and duration of oxygen supplementation within the CHF group (ρ = 0.4; P = .01).

Clinical Relevance: The increased diuretic dose and time receiving oxygen supplementation may represent increased disease severity for which NLR (and to a lesser extent PLR) may serve as a readily available marker. The data presented provide information regarding some of the systemic inflammatory changes seen in CHF secondary to MMVD in dogs. Future research should include prospective, longitudinal studies to provide insight into the long-term prognostic value of NLR and PLR in dogs with CHF.