Responses of opsonic substances to major trauma and sepsis.

Adequate opsonic capability is vital for normal host defense against infection. The presence of complement fraction 3 (C3) indicates both classical and alternative pathways of complement activation, while complement fraction 4 (C4) indicates only classical pathway activation. C-reactive protein (CRP) functions as an opsonic substance. We measured serum levels of C3, C4, and CRP in 32 trauma patients. Six suffered minor injuries and 26 suffered major injuries. Nineteen of the major-injury patients developed post-trauma sepsis. Complement levels fell immediately after injury and remained low for approximately 8 days in all patients. CRP levels rose by 12 h, peaked at 48 h, and correlated with the severity of injury and the presence of sepsis. Elevated CRP levels after 4 days postinjury indicated the presence of sepsis in all cases. CRP elevations preceded clinical diagnosis by an average of 2.4 days. Serial measurements of CRP are valuable in monitoring the course of trauma patients and may indicate the presence of septic complications before clinical detection.