The Diagnostic Accuracy of Fecal Calprotectin for Colonoscopic Abnormalities in Patients With Chronic Diarrhea

OBJECTIVE: To evaluate the diagnostic accuracy of the colloidal gold immunochromatographic assay-based fecal calprotectin (CGICA-FC) for detecting colonoscopic abnormalities in patients with chronic diarrhea. METHODS: We conducted a prospective diagnostic study across 15 centers in China. All patients with chronic diarrhea underwent colonoscopy. We quantitatively measured FC concentrations before bowel preparation and assessed diagnostic performance using ROC curve analysis. RESULTS: A total of 556 patients with chronic diarrhea and 152 nondiarrhea controls were enrolled. FC levels were significantly higher in patients with Crohn's disease, followed by ulcerative colitis and other inflammation, compared to those with high-risk adenomas, minor benign findings, normal mucosa, or nondiarrhea controls. For screening colonoscopic abnormalities from nonsignificant findings (normal mucosa & minor benign findings), the optimal cutoff was 93.8 μg/g (AUC = 0.830). FC demonstrated higher discriminatory power for colorectal inflammation (including IBD and other inflammation) with a cutoff of 118.4 μg/g (AUC = 0.896) and was most accurate for identifying IBD specifically (cutoff 157.0 μg/g, AUC = 0.929). However, its accuracy for detecting high-risk adenomas was limited (AUC = 0.587). FC showed high negative predictive value (NPV = 0.898-0.973) based on the prescreening patients with a low prior probability of abnormalities. Multivariate analysis identified colorectal inflammation and alcohol consumption as independent positive correlates with FC levels, while BMI showed a negative association. CONCLUSION: The CGICA-FC test is an accurate noninvasive tool for triaging patients with chronic diarrhea, with high diagnostic accuracy for identifying colorectal inflammation. Owing to its high NPV, it holds promise for reducing unnecessary colonoscopies in prescreening patients. CHINESE CLINICAL TRIAL REGISTRY: ChiCTR2300070117.