Correlations between quantitative assay of red cell-bound C3, serologic reactions, and hemolytic anemia.

A new immunochemical method was used to quantitate the number of C3 molecules bound to human red cells in vitro or in vivo and to assess the clinical significance of cell-bound C3 in immune hemolysis. In addition, results utilizing the immunochemical method were compared with those obtained using commonly performed semiquantitative serologic techniques such as the antiglobulin test and antiglobulin titration score. The antiglobulin test using anti-C3 antiglobulin serum became weakly positive with 60-115 molecules C3 per red cell, and was strongly positive with 1000 molecules C3 per red cell. Antiglobulin titration scores correlate well with immunochemical assessment of the number of C3 molecules per red cell. Therefore, a simple extension of the routine antiglobulin test affords clinically useful data concerning the relative degree of sensitization of red cells by C3. Two of fourteen patients with fewer than 1100 molecules C3 per red cell had hemolytic anemia, whereas 8 of 11 patients with greater than 1100 molecules C3 per red cell had overt hemolysis. The presence or absence of hemolysis was not explained by variations in the amount of IgG on these patients’ RBC. It thus appears that the amount of C3 per red cell is an important determinant of hemolysis in human immune hemolytic anemias. C OMPLEMENT COMPONENTS bound to erythrocytes in vivo have been demonstrated in certain patients with immune hemolytic anemias. Using anticomplement antiglobulin (Coombs’) reagents, complement components are found on the red cells of all patients with cold agglutinin disease”2 (which comprises about 22#{176}/a of autoimmune hemolytic anemias3), approximately 44#{176}/s of patients with warm antibody autoimmune hemolytic anemia,2 and in some patients with drug-immune hemolytic anemias,2-6 hem olytic transfusion reactions, and hemolytic disease of the newborn.7 The demonstration of red cell-bound complement components by the antiglobulin test is important in the detection and precise diagnosis of human immune hemolytic anemias.3’4 Such patients also may have low levels of serum complement and an increased fractional catabolic rate of C3,8 further implicating complement as a mediator of immune red cell destruction in vivo. The present study applied a new immunochemical method for the quantitation of the number of molecules of red cell-bound C3.9 The method was stan-