Neutrophilic myeloperoxidase index and mean light absorbance in neonatal septic and nonseptic foals

Background: Two neutrophilic indices reported by the ADVIA 120 Hematology Analyzer, neutrophilic myeloperoxidase index (MPXI), and mean light absorbance (neutrophil X mean [NXM]) have been proposed as indicators of systemic inflammatory disease in horses and of neutrophil activation in coronary ischemic syndromes in people. Objective: The aim of this study was to evaluate NXM and MPXI in healthy, sick nonseptic, and sick septic foals to determine whether conditions likely associated with neutrophil activation result in decreases in these variables. Methods: In this retrospective study, CBC data from 61 neonatal foals presented to the Equine Teaching Hospital of Barcelona were evaluated for correlations between MPXI, NXM, percentage of large unstained cells, neutrophil count, and percentage of band neutrophils. Results obtained in septic (n=32), sick nonseptic (n=22), and healthy foals (n=7) were compared. In addition, results recorded in septic/neutropenic (n=12), septic/non‐neutropenic (n=20), nonseptic/neutropenic (n=8), nonseptic/non‐neutropenic (n=14), and healthy foals (n=7) were also compared. Results: A weak negative correlation was found between MPXI and neutrophil count and between NXM and percentage of band neutrophils. Septic/neutropenic foals had significantly higher MPXI values (median 17.9, minimum–maximum 4.7–42.5) than did septic/non‐neutropenic (1.5, ?24.4 to 22.3), nonseptic/neutropenic (6.6, 0.6–17.9), and nonseptic/non‐neutropenic foals (8.8, ?10.1 to 16.8) but did not differ significantly from controls (12.8, ?8.5 to 20.4). Conclusions: Significant differences in NXM or MPXI were not found when disease groups were compared with controls; however, septic/neutropenic foals had significantly higher median MPXI than other groups of sick foals. Further prospective studies are needed to clarify if this finding is related to decreased neutrophil function or activation in septic/neutropenic foals.