CRP and ankylosing spondylitis: Depression in patients with AS is significantly correlated with measures of pathophysiology, such as the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), the Bath Ankylosing Spondylitis Functional Index (BASFI), and indicators of pain and inflammation such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) [10, 14–16].