The capacity of serum to support neutrophil phagocytosis is a vital host defense mechanism in severely injured patients.

The opsonic capacity of patient serum was studied in 43 trauma patients of whom 13 recovered uneventfully, 21 developed major infection, and nine died, mostly of infection. Blood samples were taken within 24 hours of injury. Fifteen patients were studied serially of whom 14 developed severe infection and/or died. Opsonic capacity was determined by flow cytometry and measured as the ability of normal neutrophils to phagocytose killed bacteria previously incubated with patient serum. The most dilute sera reflected changes for better and worse most clearly. On initial assessment, those who died of sepsis showed a 61% mean fluorescent intensity (MFI), which was significantly lower than the 99% MFI for those who survived infection (p less than 0.01) and the 78% MFI of those who developed no infection (p less than 0.05). Serial samples demonstrated a super serum response in four of seven patients surviving major sepsis but in none of the seven who died of infection.