The neutrophil-to-lymphocyte ratio is associated with disease severity and infectious etiologies of colitis in horses presenting with acute colitis.

Overview

• This study investigated the relationship between the neutrophil-to-lymphocyte ratio (NLR) and disease severity, survival, and infectious causes in horses presenting with acute colitis (inflammation of the colon).
• The research aimed to assess if NLR could serve as a useful biomarker to predict outcomes and identify infectious forms of colitis in horses.

Study Design and Population

• Retrospective multicenter study involving 5 equine referral hospitals.
• Included 444 horses presenting with acute diarrhea lasting less than 48 hours and 100 healthy control horses.
• Complete blood counts (hemograms) and outcome data (survival or nonsurvival) were required for inclusion.
• Infectious testing was performed when available, including tests for Salmonella spp., equine coronavirus, Clostridium spp., and Neorickettsia risticii/findlayensis.

Measurements and Definitions

• Neutrophil-to-lymphocyte ratio (NLR): The ratio of neutrophils to lymphocytes in blood, indicative of immune system activation.
• Illness severity: Assessed by the presence of systemic inflammatory response syndrome (SIRS) criteria.
• Survival outcome: Horses were categorized as survivors or nonsurvivors based on clinical records.
• Pathogen identification: Infectious causes of colitis were identified through pathogen testing.

Key Findings: NLR and Health Status

• The median NLR did not significantly differ between healthy horses (2.06) and horses with colitis (1.93).
• This suggests that simply having colitis does not necessarily alter the NLR compared to healthy individuals.

Association between NLR and Survival

• Overall, NLR was not significantly linked to nonsurvival.
• However, horses with a low NLR (<1.43) had higher odds of nonsurvival, indicating that extremely low NLR might be a marker for worse outcomes.

NLR and Illness Severity

• Horses meeting two or more SIRS criteria (more severely ill) had a lower median NLR (1.56) compared to those with fewer SIRS criteria (2.54).
• This counterintuitive finding suggests that lower NLR might reflect greater immune dysregulation or severity in acute colitis cases.

NLR and Infectious Etiologies

• Horses with identified infectious causes of colitis had lower NLR values (1.38) than those without a confirmed infectious cause (2.37).
• Among infections, equine coronavirus-infected horses exhibited the lowest median NLR (0.73), possibly reflecting a distinct immune response pattern.

Prognostic Performance

• The NLR alone showed limited ability to predict outcomes, with an area under the curve (AUC) of 0.51, which is close to random chance.
• When combined with other clinical and laboratory variables in multivariable logistic regression models, NLR contributed to improved discriminatory ability (AUC of 0.84), indicating better prediction of survival.

Clinical Implications

• The NLR by itself should not be used as a sole prognostic marker in horses with acute colitis.
• Its value lies in acting as an inexpensive, rapid, and accessible biomarker that may reflect immune system changes linked to disease severity and infectious causes.
• When used alongside other clinical assessments and lab tests, NLR may help veterinarians identify horses at greater risk of severe systemic inflammation or infectious colitis.

Conclusions

• The study highlights that lower NLR values might be indicative of more severe disease or certain infectious etiologies in equine acute colitis.
• Although not definitive on its own, incorporating NLR into a broader diagnostic and prognostic framework may aid in better management and treatment decisions for affected horses.