Activation of complement by blood transfusion filters.

Fresh blood, stored blood and granulocyte concentrates were passed through 170-micron and microaggregate blood filters to determine the degree of complement activation that occurs during transfusion of citrated blood products. Complement activation was assessed by measurement of C3 conversion using crossed immunoelectrophoresis and by assessment of C5a using a leukocyte aggregation functional assay. Prefiltration, fresh or stored blood products showed 0-1% C3 activation. Postfiltration, the degree of C3 conversion did not change for fresh blood or granulocyte concentrates. For stored whole blood, the degree of C3 conversion increased slightly to 2-3%. Prefiltration results for all samples showed a low level of C5a which did not change after passage through any filter. Serum incubated with filter material at 37 degrees C showed 2-10% C3 conversion. In contrast, results with citrated plasma showed less than 3% conversion of C3. We conclude that although some filter materials may activate complement in serum, filtration of citrated blood products through microaggregate blood filters induces little complement activation.