Changes in anti–U1 RNA antibody levels correlate with disease activity in patients with systemic lupus erythematosus overlap syndrome

Objective. To evaluate correlations between changes in anti–U1 RNA antibody levels and disease activity in 9 patients with systemic lupus erythematosus (SLE) overlap syndrome who were prospectively followed up for at least 3 years. Methods. Anti–U1 RNA antibody levels were measured quantitatively, using a nitrocellulose filter binding assay. Disease activity was measured with a validated SLE activity index. Results. All 9 major disease exacerbations were associated with peaks in anti–U1 RNA antibody level. Conclusion. These results seem to indicate that measuring anti–U1 RNA antibody levels can be useful for monitoring disease activity.