Fecal calprotectin diagnostic level gradient along the small bowel in patients with Crohn's disease.

Background and aims: Fecal calprotectin (FC) is known to be a sensitive biomarker of colonic inflammation but to a lesser degree of small bowel (SB) inflammation. Moreover, data on FC's diagnostic levels in different SB segments are scarce. We aimed to examine FC's diagnostic levels along the SB-axis in CD.

Methods: This was a post-hoc aggregated analysis of five prospective studies of adult CD patients, who underwent FC testing and SB video capsule endoscopy (VCE). Lewis score (LS) inflammation in different SB segments was tested for correlation with FC level after exclusion of colonic disease. The diagnostic levels of FC for SB inflammatory topographical-gradient were assessed using a receiver operating characteristic.

Results: 214 patients were included (age:30 [24-43] year-old, males-57%). For a similar SB inflammatory-activity (LS≥135), FC levels incrementally increased from proximal to distal SB segments (63 [30-121] versus 190 [78-549], p=0.005) and from distal SB segment to the colon (190 [78-549] versus 542 [185-1000], p=0.010). The best FC cutoffs to identify isolated mild proximal/distal SB-inflammation (LS≥135) were 77μgg and 123μgg, respectively. A cutoff of 234μgg was best to detect more significant proximal inflammation (LS≥350) when only mild distal SB-inflammation was present. In sensitivity analyses, this proximal-to-distal FC gradient was maintained when LS≥350 and LS≥790 were used as the inflammatory reference-values. Unlike FC, the magnitude of CRP elevation was unrelated to the topography of inflammation along the SB-axis.

Conclusions: FC may serve as a topographical biomarker of CD-activity, with its sensitivity to identify mucosal inflammation increases from proximal to distal SB segments.