This is a multi-national, multi-site, observational study to determine which of two strategies, when used by referring physicians is superior in the diagnosis of axial spondyloarthritis (AS) by rheumatologists.

Subjects will be selected using a non-probability sampling method. For each center of excellence, the local network of referring physicians will be assigned, according to a random code in a 1:1 ratio, to use one of the two referral strategies for eligible patients.

Inclusion Criteria:

• A subject must have back pain of unknown origin, of more than 3 months' duration, and with onset before age 45.
• A subject must be willing to give written informed consent and be able to adhere to visit schedules.

Exclusion Criteria:

• Established diagnosis of spondyloarthropathies at the time of referral.
• Any clinically significant condition or situation, other than the condition being studied, that, in the opinion of the investigator, would interfere with the study evaluations or optimal participation in the study.

Each of several participating national centers of excellence will establish a network with local primary care physicians or their equivalent who will work with the center of excellence and will provide referrals of suitable patients.