Data collection and blood indicators detection

Demographic variables including age, gender, history of common autoimmune diseases (AID, such as SLE, SS, SSc, PM, and vasculitis) were obtained. Blood examination included antinuclear antibody (ANA), cyclic citrullinated peptide (CCP), rheumatoid factor (RF), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and mutant citrulline vimentin (MCV). Elbow venous blood was extracted from all participants after fasting for 6–8 h. ANA levels were determined by an indirect immunofluorescence assay using HEp-2 cells as the substrate by a commercial kit (Euroimmun, Germany). All sections were examined independently by two experienced laboratory staff, and positive and negative control serum samples were included in each run. The analysis was performed for the most prevalent ANA patterns (nuclear homogeneous, nuclear speckled, cytoplasmic speckled, nucleolar, and centromere), and other less common ANA patterns were classified as other patterns. Only monospecific nuclear patterns were included; the primary pattern was selected for two or more patterns. Serum ANA level exceeding 1:100 was seen as positive.