For Bath Ankylosing Spondylitis Disease Activity Index 50% response (BASDAI 50), which does not include CRP, greater baseline CRP concentration predicts a BASDAI 50 response for patients with ankylosing spondylitis.22 Thus, CRP appears to be a true biological predictor, and other components of the response criteria may likewise have independent predictive value. Here, CRP is linked to ankylosing spondylitis.