Association of the neutrophil‐lymphocyte ratio with outcome in sick hospitalized neonatal foals

Abstract Background The neutrophil‐lymphocyte ratio (NLR) in human medicine is an objective biomarker that reflects prognosis. The NLR as an independent biomarker to help predict nonsurvival in hospitalized neonatal foals has not been thoroughly interrogated. Objectives/Hypothesis Retrospectively evaluate if the NLR at admission is associated with nonsurvival in sick hospitalized foals <4 days old. We hypothesized that a lower NLR will be associated with nonsurvival. Animals One thousand one hundred ninety‐six client‐owned foals <4 days old of any breed and sex: 993 hospitalized foals and 203 healthy foals. Methods Retrospective multicenter study. Medical records of foals presenting to 3 equine referral hospitals were reviewed. Foals were included if they had complete CBCs, sepsis scores, and outcome data. The NLR was calculated by dividing the absolute neutrophil count by the absolute lymphocyte count. Data were analyzed by nonparametric methods and univariate analysis. Results Of the 993 sick hospitalized foals, 686 were sick nonseptic and 307 were septic. The median NLR was lower in sick hospitalized foals (median [95% confidence interval], 3.55 [0.5‐13.9]) compared with healthy foals (6.61 [3.06‐18.1]). Septic foals had the lowest NLR (2.00 [0.20‐9.71]). The NLR was lower in nonsurviving (1.97 [1.67‐2.45]) compared with surviving foals (4.10 [3.76‐4.33]). Nonsurviving septic foals had the lowest NLR (1.47 [1.70‐3.01]). Foals with a NLR of <3.06 or <1.6 at admission had odds ratio of 3.21 (2.24‐4.29) and 4.03 (2.86‐5.67) for nonsurvival, respectively. Conclusions and Clinical Importance A NLR < 3.06 at admission in sick hospitalized foals is readily available and clinically useful variable to provide prognostic information.