Background: Following trauma and SIRS, the typical response is an elevation of the total White Cell Count (WCC) and a reduction of the lymphocyte count. This leukocytosis typically returns to normal within 48 hours. The persistence of a leukocytosis following trauma is associated with adverse outcomes. Lymphocyte anergy and dysfunction following trauma is associated with increased risk for infection and sepsis, however there is a paucity of data regarding the impact of a persistence of a low lymphocyte count in trauma patients. It is unknown whether lymphocytes return to normal levels with the rapidity of WCC, and whether a persistence of the lowered lymphocyte number impacts mortality. It was our hypothesis that a failure of the lymphocyte count to recover to normal within 4 days following is associated with an increased mortality in trauma patients.

Methods: This is a retrospective review of prospectively collected data from trauma patients collected over the 5 years of September 2003 to September 2008. Patients were included if the Injury Severity Score was >/=15, and they survived at least 3 days. Laboratory values for the first 4 hospital days were collected. White cell counts, including the subgroups of absolute neutrophil, bands, and lymphocytes counts, as well as their percentages were collected from the medical records. Demographic data, injury patterns and injury severity, and outcomes were also collected. Proportional hazards regression with time-varying covariates was used to predict time to death based on whether or not cells exited the normal range, and in those that did whether or not they returned to normal.

Results: There were 2448 patients admitted over the 5 years included in analysis. The presence of a leukocytosis following trauma was associated with a 1.7 fold increase in mortality (p=0.0045). A persistence of the leukocytosis over the 4 days following trauma increased mortality 2 fold (p<.0001) compared with patients who had an elevated white cell count that returned to normal range (4-11). A similar effect was seen with the presence of a Bandemia which was associated with a 1.7 fold increase in mortality (p<.0001), and the persistence of bandemia which independently increased mortality 2 (p<.0001). Whilst an initial lowering of the Lymphocyte number did not affect mortality, once lymphocyte count was lowered, a persistently low Lymphocyte number over the 4 days was associated with a 1.6 fold increase in mortality (p=0.0088). This finding was independent of the status of the white cell count, the neutrophils, or the bands.

Conclusion: The neutrophil portion of a SIRS response is well known and generally understood. Whilst lymphocyte anergy and dysfunction is associated with multiple organ failure and infections, there is no data addressing the pattern of lymphocytic loss in SIRS following trauma. This is the first report noting that a failure of lymphocytes to return to normal following trauma is associated with significantly higher mortality. This finding is suggestive of a mechanism whereby patients in SIRS might progress to sepsis and possible death following a traumatic mechanism.