Fecal calprotectin is a widely used non-invasive biomarker to assess intestinal inflammation in Crohn’s disease (CD). However, its reliability may vary depending on the anatomical location of disease involvement. 

The objective of this study was to investigate the correlation between disease location, fecal calprotectin levels, and endoscopic disease activity measured by the Crohn’s Disease Endoscopic Index of Severity (CDEIS).

We conducted a retrospective study including 172 patients with Crohn’s disease who underwent both fecal calprotectin testing and ileocolonoscopy with CDEIS scoring. 

Disease locations were classified according to the Montreal classification: L1 (ileal), L2 (colonic), L3 (ileocolonic), L4 (upper gastrointestinal), and L3L4 (combined ileocolonic and upper GI involvement).

Statistical analyses were performed using Jamovi software. Spearman’s rank correlation was used to assess the relationship between fecal calprotectin and CDEIS scores, both globally and stratified by disease location. Comparisons of calprotectin and CDEIS values across locations were made using the Kruskal-Wallis test, as data were not normally distributed.

Among the 172 patients included, fecal calprotectin demonstrated a moderate and statistically significant correlation with endoscopic activity across the entire cohort (Spearman’s ρ = 0.53, p < 0.001). When analyzed by disease location, the strongest correlations were observed in colonic disease (L2: ρ = 0.62) and combined ileocolonic and upper GI involvement (L3L4: ρ = 0.76). Ileal disease (L1) showed a moderate correlation (ρ = 0.41), while isolated ileocolonic (L3: ρ = 0.30) and upper GI disease (L4: ρ = 0.26) showed weaker associations. A perfect correlation in the L1L4 subgroup (ρ = 1.00) was noted but was limited by the very small sample size. Despite these differences, Kruskal-Wallis tests revealed no statistically significant differences in calprotectin levels (p = 0.99) or CDEIS scores (p = 0.89) across the various disease locations.

Fecal calprotectin demonstrates a good overall correlation with endoscopic disease activity in Crohn’s disease, reinforcing its usefulness as a monitoring tool regardless of disease location. Although stronger correlations were noted in colonic and extended disease forms, no statistically significant differences were found across locations. These findings suggest that fecal calprotectin can be reliably used as a location-independent marker of mucosal inflammation in Crohn’s disease.