Changes in equine complete blood count parameters and inflammatory indices with inflammation

Abstract

Early detection of inflammation is valuable in preserving horse health and limiting progression of disease. Metrics that reflect inflammation using a common test such as a complete blood count (CBC) would therefore be beneficial. The hypothesis of this study was that cell populations and indices accounting for numerous CBC parameters would differ between horses at different levels of inflammation. The objective is to provide better reference intervals for veterinarians. Concentrations of serum amyloid A (SAA), C-reactive protein (CRP), and haptoglobin from clinically healthy horses (n = 153) and horses seeking veterinary care (n = 46) were quantified using ELISA and peroxidase assays. Literature values of biomarker concentrations were used to establish inflammatory groups: inflamed (I; CRP n = 87, SAA n = 21, haptoglobin n = 41) or not inflamed (N; CRP n = 112, SAA n = 178, haptoglobin n = 158). The IDEXX ProcyteDx was used to obtain CBCs. Inflammatory indices were calculated from CBC outputs. Data were analyzed using the Kruskal–Wallis test with Dunn's post hoc analysis and a Bonferroni correction. A modified Levene's test was used to determine differences in variance, defined as the deviation of data points from the median of each group, to identify differences in the spread of parameter outputs between groups. Significance was set at P < 0.05. Horses in group I had higher median systemic inflammatory response index (SIRI), systemic inflammatory index (SII), and aggregate index of systemic inflammation (AISI) values with greater variance than group N for SAA (P < 0.01) and haptoglobin (P < 0.03). Horses with SAA and haptoglobin concentrations in group I exhibited greater variance of white blood cells (P < 0.01), neutrophil percentage (P < 0.01), neutrophils (P < 0.01), lymphocyte percentage (P < 0.01), monocyte percentage (P < 0.01), neutrophil-lymphocyte ratio (P < 0.01), and platelet-lymphocyte ratio (P < 0.01) than group N. The CRP inflammatory group was not associated with differences in CBC parameters, suggesting SAA and haptoglobin may be more valuable in measuring inflammation related to hematological changes. Many differences in medians and variation occurred within industry-accepted reference intervals. This suggests an opportunity to adjust these intervals to detect inflammation. These results identify CBC parameters and calculated indices that may be valuable in the detection of inflammation.