Objective. We examined the clinical relationship between human leukocyte antigen B27 (HLA-B27) and juvenile idiopathic arthritis (JIA). Additionally, we assessed the usefulness of the Assessment of SpondyloArthritis International Society (ASAS) criteria for diagnosing juvenile spondyloarthropathies (SpA). Methods. We retrospectively reviewed medical records of 239 patients with JIA classified according to the International League of Associations for Rheumatology (ILAR) classification to analyze the features of the joint involvement site. Results were correlated with the presence of HLA-B27. After that, we classified the 239 JIA patients according to the ASAS criteria to diagnose juvenile SpA. The relationship between the ASAS criteria and a diagnosis of juvenile SpA was analyzed by a chi-squared test. Results. Back pain was associated with HLA-B27 in boys (p=0.002) but not in girls (p=0.616). In both sexes, involvement of the small joints in the lower extremities was highly associated with HLA-B27 (p=0.001 for boys, p=0.021 for girls). In addition, HLA-B27 was associated with enthesitis (p=0.004 for boys, p=0.021 for girls). Eighty-seven (36.4%) patients with JIA fulfilled the ASAS criteria; 2 (0.8%) had axial SpA and 85 (35.6%) had peripheral SpA. HLA-B27 was the most significant factor for diagnosing juvenile SpA (sensitivity 80%, specificity 99.31%, positive likelihood ratio, 116). Conclusion. The ILAR criteria have some weaknesses for diagnosing HLA-B27-positive JIA patients in early stages. The use of the ASAS criteria for juvenile patients will enable pediatric rheumatologists to diagnose juvenile SpA patients earlier.

Keywords: Juvenile arthritis, HLA-B27 antigen, Ankylosing spondylitis, Spondylarthropathies