Diagnostic and classification criteria are very important to institute in clinical medicine. Diagnostic criteria are broad and heterogenous; they include subjective symptoms, physical exam findings and objective tests that are used routinely in the clinic to help diagnose a condition and guide patient’s care. Classification criteria are usually standardized and homogenous; while some clinicians use them to aid in patient care, they are intended to create well-defined patient cohorts for clinical research. There are currently no diagnostic criteria in the field of axial spondyloarthritis. We list below several classification criteria, the most commonly used are the modified New York and the ASAS criteria.

In 1961, criteria were defined for the first time to classify Ankylosing Spondylitis; it was known as Rome criteria (Kellgren 1963).  In this set of criteria, no correction was made for the effects of age and sex on chest and spinal mobility. Although the radiographic criterion was given a greater weight than the clinical criteria (3 times), a diagnosis of AS was still possible based solely on clinical criteria, without any radiographic evidence.

In 1966, the New York criteria (Bennett and Wood 1968) were introduced, which tweaked some of the Rome criteria. In the New York criteria, it was mandatory to have a radiographic criterion +/- clinical criteria. The presence of clinical criteria along with the radiographic one would give a diagnosis of definite AS; while the absence of clinical criteria would give a diagnosis of probable AS. In the clinical criteria, major changes were specifying spine planes where the motion is limited, quantifying the limitation in chest expansion, and omission of the iritis/eye inflammation criterion that was present in the Rome criteria.