Neutrophil phenotyping reflects injury severity when base excess and lactate remain normal.

INTRODUCTION: Accurate assessment of injury severity is essential for optimal trauma care, as it dictates timing and intensity of interventional strategy. Conventional markers, such as base excess and lactate levels are usually borderline deranged in patients with midrange injury severity. This study explored whether determining circulating neutrophil phenotypes in these patients (ISS 9-35) might aid in the assessment of injury severity. METHODS: A descriptive single-center cohort study of trauma patients ≥ 16 years between 2013 and 2023 was conducted. Data was collected from the Dutch National Trauma Registry and the Utrecht Patient-Oriented Database (< 10% missing values). Base excess, lactate levels and neutrophil phenotypes were routinely measured in emergency department blood samples. The dynamics of these parameters was analyzed in the context of increasing Injury Severity Scores (ISS). RESULTS: 807 patients were included, of whom 591 were classified as midrange severely injured. In these patients, banded neutrophils showed a greater fold increase between ISS 9 and 35 compared with base excess and lactate (6.7, 2.7, and 1.5, respectively). Furthermore, the number of banded neutrophils exceeded the upper interquartile range of controls at lower trauma severities compared to base excess or lactate (ISS 17 vs. 30 and 39, respectively). DISCUSSION: Although base excess and lactate perform well as indicators of physiological derangement in severe trauma (ISS > 35), increased numbers of banded neutrophils are detectable at lower ISS levels and rise more rapidly than conventional chemistry markers in midrange severely injured patients. As such, neutrophil phenotyping can complement traditional physiological markers in injury burden assessment in midrange severely injured patients.