Diagnostic accuracy of faecal calprotectin in patients with active perianal fistulas

Abstract

Background: Faecal calprotectin (FC) is a marker of mucosal inflammation.

Objective: The aim of this study was to determine the diagnostic accuracy of FC to (a) differentiate between perianal fistulizing Crohn's disease (pCD) and cryptoglandular perianal fistulas; and (b) detect mucosal inflammation in pCD.

Methods: Patients with active perianal fistulas who had FC measured and a complete ileocolonoscopy within 10 weeks were retrospectively included.

Results: Fifty-six patients were included (pCD, n = 37) of whom 19 pCD patients exhibited ulcers. FC was significantly higher in pCD compared to cryptoglandular fistulas (µg/g) (708.0 (207.0-1705.0) vs 32.0 (23.0-77.0), p < 0.001). Area-under-the-curve (AUC) value for FC receiver operating characteristic (ROC) statistics was 0.900. Optimal FC cut-off was ≥ 150 µg/g. To differentiate pCD from cryptoglandular fistulas in the absence of luminal inflammation, optimal cut-off remained ≥ 150 µg/g (AUC = 0.857, sensitivity = 0.81, specificity = 0.89, positive predictive value (PPV) = 93.8% and negative predictive value (NPV) = 70.8%). In pCD, FC was significantly increased in the presence of ulcers (1672.0 vs 238.0, p = 0.004). Optimal cut-off was ≥ 250 µg/g (AUC = 0.776; sensitivity = 0.89, specificity = 0.56, PPV - 68.0% and NPV = 83.0%).

Conclusion: FC discriminates pCD from cryptoglandular fistulas, even in the absence of intestinal ulcers. In active pCD, an elevated FC does not accurately predict the presence of ulcers and should be interpreted with caution.

Keywords: Crohn's disease; Faecal calprotectin; biomarker; diagnostic accuracy; perianal fistula.

Figure 1.

Flow diagram of patient selection.

Figure 2.

Diagnostic accuracy of faecal calprotectin in patients with an active perianal fistula. (a) Left: individual faecal calprotectin levels in the two groups of active perianal fistulas (perianal fistulizing Crohn's disease, n = 37; cryptoglandular fistulas, n = 19); right: receiver operating characteristic curve for the ability of faecal calprotectin to differentiate between perianal fistulizing Crohn's disease and cryptoglandular perianal fistulas. (b) Left: individual faecal calprotectin levels in the two groups of active perianal fistulas (perianal fistulizing Crohn's disease, n = 18; cryptoglandular fistulas, n = 19) within a subpopulation of patients without ulcers; right: receiver operating characteristic curve for the ability of faecal calprotectin to differentiate between perianal fistulizing Crohn's disease and cryptoglandular perianal fistulas within a subpopulation without ulcers. (c) Left: individual faecal calprotectin levels in perianal fistulizing Crohn's disease patients according to the presence of ulcers (perianal fistulizing Crohn's disease with ulcers, n = 19; perianal fistulizing Crohn's disease without ulcers, n = 18); right: receiver operating characteristic curve for the ability of faecal calprotectin to discriminate between the presence or absence of intestinal ulcers in perianal fistulizing Crohn's disease patients with an active perianal fistula. AUC, area under the curve; CG: Cryptoglandular; CI, confidence interval; pCD: perianal fistulizing Crohn's disease; ROC: receiver operating characteristic.