The ASAS classification criteria are a set of diagnostic guidelines established by the Assessment of SpondyloArthritis international Society for identifying axial spondyloarthritis (axSpA), which includes ankylosing spondylitis. These criteria are crucial in clinical practice as they facilitate early diagnosis and appropriate management, potentially improving patient outcomes. A key association is the presence of HLA-B27 antigen, which is commonly found in individuals with axSpA.