 The burden and risks associated with participation are minimal. No medical intervention is taken place. If the GP of the patients is randomized to the referral model, the patient is checked for the risk of axial spondyloarthritis, by the non-invasive referral model. If the referral model is positive a referral to the rheumatologist is advised. Is the GP is randomized to the usual care there is no difference in the treatment of low back pain than nowadays. A GP is still allowed to treat the CLBP patients optimal and a referral to the rheumatologist is allowed but not actively advised. 