TOPLINE

A rapid fecal calprotectin (FC) assay accurately distinguished colonoscopic abnormalities from normal mucosa and minor benign findings at a cutoff of 93.8 μg/g and performed even better at flagging colorectal inflammation and inflammatory bowel disease (IBD), supporting its use as a noninvasive rule-out tool in patients with chronic diarrhea.

METHODOLOGY

• Researchers conducted a prospective diagnostic study across 15 clinical centers in China between March 2023 and April 2025 to assess the diagnostic accuracy of FC for detecting colonoscopic abnormalities in patients with chronic diarrhea and to examine factors associated with FC levels.
• The study included 556 patients with chronic diarrhea (mean age, 44.6 years; 36.7% women) with no prior definitive diagnosis or treatment, who underwent colonoscopy, and provided stool samples before bowel preparation for FC quantification; 152 control individuals without diarrhea (mean age, 44.4 years; 39.5% women) were also included.
• Chronic diarrhea was defined as loose or watery stools and/or bowel movement frequency of at least twice daily for at least 4 weeks without a confirmed etiology at enrollment.
• FC concentrations were quantified using a rapid colloidal gold immunochromatographic assay with collected stool samples obtained within 24 hours before colonoscopy and before bowel preparation; results were available within 15 minutes.
• Colonoscopy was performed by experienced gastroenterologists blinded to FC results, and biopsies were taken from suspicious lesions as needed; the diagnostic performance of FC was then evaluated against colonoscopic findings.

TAKEAWAY

• FC levels were substantially higher in patients with Crohn’s disease (median, 397.9 μg/g) than in those with ulcerative colitis (median, 259.3 μg/g) and other forms of colitis (median, 198.4 μg/g), whereas FC levels were substantially lower in patients with high-risk adenomas (median, 87.2 μg/g), minor benign findings (54.0 μg/g), or normal mucosa (59.5 μg/g) and in control individuals without diarrhea (43.3 μg/g).
• An optimal FC cutoff of 93.8 μg/g distinguished colonoscopic abnormalities from nonsignificant findings (minor benign findings plus normal mucosa), achieving an area under the receiver operating characteristic curve (AUC) of 0.830, with a sensitivity of 81.9%, specificity of 71.2%, and negative predictive value (NPV) of 89.8%.
• Diagnostic accuracy for distinguishing colorectal inflammation improved at an FC cutoff of 118.4 μg/g (AUC, 0.896; sensitivity, 87.1%; specificity, 78.4%; NPV, 95.0%). The FC assay also showed high accuracy for distinguishing IBD at a cutoff of 157.0 μg/g (AUC, 0.929; sensitivity, 88.5%; specificity, 85.5%; NPV, 97.3%) and for other forms of colitis at a cutoff of 108.6 μg/g (AUC, 0.840) but showed limited accuracy for detecting high-risk adenomas (AUC, 0.587).
• In multivariable analysis, higher FC levels were independently associated with colorectal inflammation and alcohol consumption, whereas BMI was associated with lower FC levels (P < .05 for all).

IN PRACTICE

“Our findings underscore that FC is more suitable as a ‘rule-out’ test in this real-world clinical setting. This characteristic is advantageous for a screening tool as a negative result can provide clinicians and patients with confidence to defer or forego more invasive investigations, such as colonoscopy,” the authors of the study wrote.

SOURCE

The study was led by Xinghuang Liu, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China. It was published online in the Journal of Gastroenterology and Hepatology.

LIMITATIONS

The study was not large enough to fully assess how well FC works across all possible causes of abnormal colonoscopy findings. Use of colonoscopy and biopsy as the reference standard may have missed microscopic inflammation or introduced sampling-related misclassification. The diagnostic workup focused on colonoscopy and did not include other complementary evaluations for chronic diarrhea such as upper endoscopy or stool cultures.

DISCLOSURES

The study was funded by the National Key Research and Development Program of China, the National Natural Science Foundation of China, and Xiamen Wiz Biotech Co., Ltd.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.