A new, highly sensitive assay for C-reactive protein can aid the differentiation of inflammatory bowel disorders from constipation- and diarrhoea-predominant functional bowel disorders

BACKGROUND: Patients presenting to gastroenterology clinics with symptoms suggestive of lower-bowel disorders often require extensive investigation to differentiate functional from organic disease. C-reactive protein (CRP) is a sensitive marker of systemic inflammation. Levels of CRP are frequently raised in cases of inflammatory bowel disease (IBD). However, using conventional assays, not all cases of IBD have a detectable level. OBJECTIVE: To determine whether a new highly sensitive CRP enzyme-linked immunosorbent assay (ELISA) can aid the differentiation between IBD and functional bowel disorders (FBDs) in gastroenterology outpatients presenting with lower-bowel symptoms. METHODS: Serum was taken from 224 subjects attending a gastroenterology outpatient clinic. Of these, 203 were new patients and 21 were follow-up patients with quiescent colitis. The serum was analysed using a sensitive in-house ELISA. All new patients had a rigid sigmoidoscopy and rectal biopsy. Patients were investigated as deemed appropriate by the attending physician. Notes were reviewed after at least 6 months to determine the final diagnosis. RESULTS: A cut-off value of 2.3 mg/l had a sensitivity of 100% and a specificity of 67% in differentiating FBD from new cases of IBD. The geometric mean CRP was 0.383 mg/l in the constipation-predominant FBD group, 1.435 mg/l in diarrhoea-predominant FBD, 1.455 mg/l in quiescent IBD, 8.892 mg/l in newly presenting cases of ulcerative colitis, and 13.123 mg/l in newly presenting cases of Crohn's disease. CONCLUSION: A new, highly sensitive assay for CRP may help to distinguish FBD from IBD.