Fecal Calprotectin and Segmental Inflammation in Small Bowel Crohn's Disease: A Capsule Endoscopy-Based Study

Background/Objectives: The correlation between fecal calprotectin (FC) levels and small bowel (SB) inflammation in Crohn's Disease (CD) remains a subject of debate. This study aims to investigate the association between FC and SB inflammatory activity. Methods: Retrospective cohort study involving patients with SB-CD who underwent small bowel capsule endoscopy (SBCE) and FC testing, excluding those with colonic inflammation. Patients were categorized based on the Lewis Score (LS): no inflammation (all SB tertiles with LS < 135); proximal SB inflammation (first and/or second tertiles with LS ≥ 135, without inflammation in the third tertile); distal SB inflammation (third SB tertile with LS ≥ 135, no inflammation in the proximal SB); or pan-SB inflammation (proximal and distal SB with inflammation). Results: Eighty-seven patients were included (median age 35 years, 75.9% female). Inflammation was absent in 21.8% of patients, proximal inflammation in 4.6%, distal inflammation in 33.3% and pan-SB inflammation in 40.4%. FC median values exhibited an ascending trend along the SB: no inflammation 58 µg/g; proximal SB inflammation 65 µg/g; distal SB inflammation 122 µg/g; or pan-SB inflammation 400 µg/g. FC correlated with LS in the second (ρ = 0.464) and third tertiles (ρ = 0.435), but not in the first tertile. FC levels were significantly higher in pan-SB disease compared to isolated proximal (p = 0.014) and distal inflammation (p = 0.012). A cutoff of 178 µg/g differentiated pan-SB from isolated distal disease (AUC = 0.716; sensitivity 85.7%, specificity 58.6%). Conclusions: FC levels correlate positively with the presence of SB lesions in the second and third tertiles. However, it is not a reliable marker for detecting inflammation in the first tertile, highlighting the importance of performing a SBCE in these patients.