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

OBJECTIVE

To evaluate associations between the neutrophil-to-lymphocyte ratio (NLR), nonsurvival, illness severity, and infectious etiologies.

METHODS

This was a retrospective multicenter study that included 100 healthy horses and 444 horses presenting with acute diarrhea to 5 equine referral hospitals. Inclusion criteria were diarrhea duration < 48 hours, complete hemograms, and outcome data. Illness severity was assessed using systemic inflammatory response syndrome. The results of pathogen testing for Salmonella spp, equine coronavirus, Clostridium spp, and Neorickettsia risticii/findlayensis were reviewed when available. Data were analyzed using nonparametric statistics and univariate and multivariable logistic regression models.

RESULTS

Median NLR [IQR] did not differ between healthy horses (2.06 [1.43 to 2.58]) and horses with colitis (1.93 [0.86 to 3.76]). The NLR was not significantly associated with nonsurvival; however, horses with an NLR < 1.43 demonstrated higher odds of nonsurvival. Horses meeting ≥ 2 systemic inflammatory response syndrome criteria had a lower NLR (1.56 [0.69 to 2.85]) compared with those meeting 0 to 1 criteria (2.54 [1.08 to 4.70]). Horses with an identified infectious cause had lower NLR than those without (1.38 [0.78 to 2.98] vs 2.37 [0.92 to 4.00]), with the lowest NLR observed in equine coronavirus-infected horses (0.73 [0.40 to 1.56]). The NLR alone had limited prognostic performance (area under the curve, 0.51), but multivariable models with NLR had good discriminatory ability (area under the curve, 0.84).

CONCLUSIONS

While NLR alone is insufficient as a prognostic marker, it may reflect underlying immune dysregulation that contributes to disease severity.

CLINICAL RELEVANCE: The NLR is an inexpensive, readily available biomarker that may help clinicians identify horses at risk of severe systemic inflammation and identify infectious colitis when interpreted with other clinical and laboratory findings.