Methods: Orthopedists and primary care physicians were offered to refer patients with i) chronic low back pain (duration >3 months) and ii) onset of back pain at an age < 45 years to a specialized rheumatology outpatient clinic for further diagnostic work-up if at least one of the following screening parameters was present: 1) inflammatory back pain (IBP), 2) positive HLA-B27, 3) sacroiliitis as detected by imaging. The final diagnosis was made according to expert opinion.