Quantitative studies have shown that Mg++ and Ca++ each have specific roles in C′ activity, the Mg++ enhancing hemolytic activity, the Ca++ protecting the reagent from decay. Although addition of Mg++ alone significantly increased C′ activity, this was offset by a marked reduction of stability. Concomitant addition of Ca++, however, overcame the lability conferred by Mg++. The findings indicated that optimal concentrations of both cations in complement fixation would provide maximum hemolytic activity and stability of C′, and minimize possible adverse effects due to uncontrolled amounts of endogenous cations in test reagents. A relative excess of either cation inhibited the activity of the other. Thus, addition of one cation alone, particularly Mg++, to diagnostic tests seemed strongly contraindicated.
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