CRP and Arthritis: Suboptimal response is usually based on signs and symptoms of CD (such as weight loss, diarrhea, abdominal pain), extraintestinal manifestations (e.g., iritis or arthritis), use of symptomatic treatments (e.g., for diarrhea or pain), blood test parameters (e.g., systemic markers of inflammation such as C-reactive protein [CRP]), and patient general well-being.