Is interleukin 6 an early marker of injury severity following major trauma in humans?

Hypothesis: Interleukin 6 (IL-6), a multifunctional cytokine, is expressed by various cells after many stimuli and underlies complex regulatory control mechanisms. Following major trauma, IL-6 release correlates with injury severity, complications, and mortality. The IL-6 response to injury is supposed to be uniquely consistent and related to injury severity. Therefore, we designed a prospective study starting as early as at the scene of the unintentional injury to determine the trauma-related release of plasma IL-6 in multiple injured patients. Patients and Methods: On approval of the local ethics committee, 94 patients were enrolled with different injuries following trauma (Injury Severity Score [ISS] median, 19; range, 3-75). The patients were rescued by a medical helicopter. Subsets were performed according to the severity of trauma-4 groups (ISS, <9, 9-17, 18-30, and >32)-and survival vs nonsurvival. The first blood sample was collected at the scene of the unintentional injury before cardiopulmonary resuscitation, when appropriate. Then, blood samples were collected in hourly to daily intervals. Interleukin 6 plasma levels were determined using a commercial enzyme-linked immunosorbent assay test. The short-term phase protein, C-reactive protein, was measured to characterize the extent of trauma and to relate these results to IL-6 release. Results: As early as immediately after trauma, elevated IL-6 plasma levels occurred. This phenomenon was pronounced in patients with major trauma (ISS, >32). Patients with minor injury had elevated concentrations as well but to a far lesser extent. In surviving patients, IL-6 release correlated with the ISS values best during the first 6 hours after hospital admission. All patients revealed increased C-reactive protein levels within 12 hours following trauma, reflecting the individual injury severity. This was most pronounced in patients with the most severe (ISS, >32) trauma. Conclusions: To our knowledge, this is the first study that elucidates the changes in the IL-6 concentrations following major trauma in humans as early as at the scene of the unintentional injury. The results reveal an early increase of IL-6 immediately after trauma. Moreover, patients with the most severe injuries had the highest IL-6 plasma levels. There is strong evidence that systemic IL-6 plasma concentrations correlate with ISS values at hospital admission. Therefore, IL-6 release can be used to evaluate the impact of injury early regardless of the injury pattern.