A quantitative measurement of complement (C3) activation in severely burned patients

Circulating levels of native C3 (C3B) and plasma C3d were determined during the hospital course of 27 thermally injured patients (mean TBSA 56%, range 30% to 96%). Assessment of C3 activation/degradation and its synthetic rate was performed by means of the C3 activation index (reflecting C3d to C3B ratio). The mean value of C3B decreased during the first 72 hours postburn but subsequently returned to normal or supranormal levels. No correlation was found between the circulating C3B and EDTA-plasma C3d levels. In most patients, increased C3 consumption occurred during the acute postburn period. The C3 activation index did not correlate with the extent of the injury but was higher in survivors than in nonsurvivors. The C3 activation index was increased during sepsis, whereas C3B levels were decreased. In recovering burns, C3d and C3B levels were normal or moderately elevated, since an increased C3 synthetic rate accompanied its increased catabolism. In a few cases, a low C3 activation index observed even during septic episodes may suggest decreased C3 conversion rate. Our findings confirm that both excessive C3 consumption and the low C3 activation rate may be observed among complement alterations following burn trauma.