Introducción:

Anti-C1q autoantibodies have been proposed as useful marker in systemic lupus erythematosus due to their association with lupus nephritis.

Objective:

To determine the prevalence of anti-C1q in patients with systemic lupus erythematosus and other rheumatic diseases to evaluate the association with lupus nephropathy.

Methods:

One hundred seventy-nine patients with systemic lupus erythematosus and 82 with other rheumatic diseases were included. Lupus nephritis was diagnosed in 70 (39%) of patients with systemic lupus erythematosus. Anti-C1q IgG antibodies were determined by ELISA. Associations were evaluated by logistic regression analysis.

Results:

The prevalence of anti-C1q was 37% (66/179) in patients with systemic lupus erythematosus and 9% (7/82) in controls (OR = 6.3; 95% CI 2.8-14). .1; p < 0.001). Anti-C1q was associated with proteinuria (OR = 2.6; 95% CI 1.2-6.0; p < 0.022); elevated erythrocyte sedimentation rate (OR = 3.2; 95% CI 1.5-6.7; p < 0.003) and anti-dsDNA (OR = 3.9; 95% CI 1.7-9.1; p < 0.002). In the logistic regression model adjusted for demographics and anti-dsDNA, although the OR of anti-C1q for nephritis was 2-fold higher than in the absence of anti-C1q, it only approached statistical significance. Simultaneous positivity of anti-C1q and anti-dsDNA was associated with lupus nephritis (OR = 4.3; 95% CI 1.9-9.5; p < 0.001).

Conclusions:

Anti-C1q occurred more frequently in patients with systemic lupus erythematosus than in controls. Anti-C1q combined with anti-dsDNA was strongly associated with lupus nephritis.

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