Time for new concepts about measurement of complement activation by cardiopulmonary bypass? 
Fifty-one patients admitted for routine coronary bypass operations were randomized to cardiopulmonary bypass with a membrane oxygenator (Capiox) or a bubbler (Polystan or William Harvey).  Complement activation was measured using enzyme immunoassays for concentrations of C3 activation products and the terminal complement complex.  From 5.8 to 8.1 arbitrary units (AU)/mL (medians), the plasma concentrations of C3 activation products increased by 119.9 AU/mL (Capiox), 124.6 AU/mL (Polystan), and 79.5 AU/mL (William Harvey) to a peak at closure of the sternum (not significant when related to baseline concentrations).  The increase in C3 activation products and baseline C3 activation were linearly correlated (R2 = 0.30; p less than 0.0001).  From 5.5 to 6.1 AU/mL, the plasma terminal complement complex concentrations increased by 45.2 AU/mL (Capiox), 15.4 AU/mL (Polystan), and 17.4 AU/mL (William Harvey) to a peak before termination of cardiopulmonary bypass.  Maximal terminal (C5-C9) activation was significantly higher in the membrane oxygenator group (p less than 0.0001) and showed no relationship to C3 activation.  Measurement of C3 activation only gives no information about C5-C9 activation.  At present, terminal complement complex quantitation is probably the best index of C5-C9 activation during cardiopulmonary bypass.