Sensitivity and specificity of Interleukin 29 in patients with rheumatoid arthritis and other rheumatic diseases

•Patients with rheumatoid arthritis (RA) have high serum levels of IL-29.•Serum IL-29 levels correlate with rheumatoid factor and absolute neutrophil count.•IL-29 has high specificity and moderate sensitivity to identify RA patients.•IL-29 may be a biomarker in autoimmune diseases specially in RA. Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic and progressive inflammation that can cause a high degree of disability in affected individuals. Proinflammatory cytokines play central roles in the development of degradative and inflammatory responses in RA. IL-29 has been identified in RA and reported as a biomarker of the disease. To analyze serum levels and accuracy of IL-29 in RA patients compared to healthy subjects and patients with other rheumatic diseases. IL-29 serum levels were measured in 121 patients with RA, 53 patients with systemic lupus erythematosus (SLE), 60 patients with systemic sclerosis (SSc), 29 patients with fibromyalgia (FM), 50 patients with osteoarthritis (OA) and 68 healthy individuals as controls. IL-29 levels in serum were investigated by ELISA. Sensitivity, specificity and likelihood ratios (LR) for having RA were calculated. Serum levels of IL-29 were increased in RA patients 113.6 (IQR = 31.25–308.5) pg/ml compared to non-RA patients (SLE, SSc, OA, and FM) (31.25 pg/ml) and healthy controls (31.25 pg/ml, p