In SLE, anti-C1q autoantibodies are found in up to 50% of patients. However, more than 95% of the patients with lupus nephritis have such antibodies. Anti-C1q autoantibodies are relevant for the follow-up monitoring of lupus patients. Typically an increase in the titer of anti-C1q autoantibodies can be observed between a few weeks and 6 months before a flare of lupus nephritis occurs. Patients without anti-C1q autoantibodies have a very low risk of developing active lupus nephritis within the following 6 months. In contrast, high titers of anti-C1q autoantibodies are not necessarily predictive of a renal flare. However, patients with high or increasing titers of anti-C1q autoantibodies are at 50% risk to develop an active lupus nephritis, particularly if they have suffered from lupus nephritis in the past. A successful treatment of active lupus nephritis typically decreases the titer of anti-C1q autoantibodies. The titers of anti-C1q autoantibodies can drop below the lower limit of detection and remain undetectable even after reduction or termination of immunosuppression.

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