Do normal fecal calprotectin, negative lactoferrin, absent stool white blood cells, and low EPX argue against intestinal inflammation?

Evaluating non-invasive fecal biomarkers offers a highly reliable method to differentiate organic gastrointestinal pathology from functional bowel disorders in symptomatic patients.

Clinical evidence for neutrophilic inflammation

• Fecal Calprotectin: A normal result ($<50\ \mu\text{g/g}$) provides an exceptional negative predictive value (NPV) of 95% to 99% for ruling out active inflammatory bowel disease (IBD) and other significant neutrophilic mucosal pathologies, strongly supporting a functional bowel disorder diagnosis.
• Fecal Lactoferrin: A negative result ($<7.25\ \mu\text{g/g}$) carries an NPV of 78% to 100%, indicating an absence of active, clinically significant neutrophilic intestinal inflammation.
• Stool White Blood Cells: While the absence of stool leukocytes is consistent with a lack of acute inflammation, this marker is highly unstable and lacks the diagnostic sensitivity of calprotectin or lactoferrin, meaning it cannot independently exclude chronic invasive pathology.

Mechanistic insights into eosinophilic inflammation

• Eosinophil Protein X (EPX): EPX is a specific granule protein released directly into the gut lumen during active eosinophilic activation and degranulation.
• Inflammatory Activity: Low or undetectable stool EPX levels indicate a lack of active degranulation, arguing against active eosinophilic colitis, active microscopic colitis (particularly collagenous colitis), and mucosal eosinophilia.
• Clinical Limitations: Because eosinophilic mucosal infiltration can be patchy or highly localized, low fecal EPX cannot completely exclude localized tissue eosinophilia without histopathological confirmation via mucosal biopsy.

Bottom line

• Normal fecal calprotectin, negative lactoferrin, and low EPX strongly argue against active, invasive neutrophilic or eosinophilic intestinal inflammation, pointing instead toward a functional bowel disorder; however, histopathology remains necessary to definitively rule out patchy mucosal disease.