Comparison of the complement-fixing activity of antinuclear antibodies in lupus nephritis, mixed connective tissue disease, and scleroderma.

Complement-fixing antinuclear antibody (CFANA) titers were measured in 18 patients with lupus nephritis and were compared to titers in 22 patients with scleroderma and mixed connective tissue disease (MCTD) who had comparable ANA titers but lacked nephritis. CFANA titers were higher in SLE patients with nephritis than in a control group of SLE patients without nephritis but were no higher than in scleroderma or MCTD. Thus the striking differences in the prevalence of nephritis among these patients with high titer ANA cannot be explained by differences in complement fixation by these antibodies.