Objective Immunoglobulin G (IgG) autoantibodies in systemic lupus erythematosus (SLE) are considered pathogenic, whereas immunoglobulin M (IgM) autoantibodies may have protective effects. The aim of this study was to identify whether IgG/IgM autoantibody ratios differ between patients with incomplete systemic lupus erythematosus (iSLE), patients with SLE, and healthy controls (HCs), and whether IgG/IgM autoantibody ratios relate to progression from iSLE to SLE.