 Rationale: Axial spondyloarthritis axSpA is an inflammatory back pain disorder affecting up to 24 of young chronic low back pain CLBP patients. For general practitioners GPs it is difficult to distinguish axSpA patients in the large amount of CLBP patients. In previous studies a referral rule for axSpA applicable in CLBP patients was developed and validated. The next step is to investigate the impact of the referral rule in daily practice. This impact analysis will test if the referral rule will be beneficial or harmful. 