Fecal Calprotectin Correlates With Disease Extent but Remains a Reliable Marker of Mucosal Healing in Ulcerative...

Fecal calprotectin (FC) is a marker of mucosal inflammatory activity in ulcerative colitis (UC). FC levels may also be influenced by the extent of disease. We aimed to examine the relationships between FC, mucosal activity, and disease extent and to assess how disease extent affects the diagnostic accuracy of FC.

We conducted a single-center observational study of patients with UC. Mucosal inflammatory activity was rated by the Mayo Endoscopic Score (MES) and Nancy Histological Index (NHI). The endoscopic and histological extents of disease were categorized by the Montreal classification and colorectal distribution of histologically active inflammation (NHI ≥ 2), respectively. FC was measured by EliA Calprotectin Enzyme fluoroimmunoassay (Phadia).

A total of 518 visits by 254 patients were analyzed. In endoscopically active UC (MES ≥ 2), FC levels were significantly lower in proctitis (440 [interquartile range (IQR) 175-1,350] mg/kg) as compared with left-sided colitis (840 [IQR 298-2,011] mg/kg, P = 0.048) or pancolitis (1,690 [IQR 723-2,582] mg/kg, P = 0.00005). In MES ≤1, FC levels were significantly higher in pancolitis (85 [IQR 43-350] mg/kg) as compared with proctitis (24 [IQR 15-116] mg/kg, P = 0.00032) or left-sided colitis (40 [IQR 15-160] mg/kg, P = 0.012). However, FC remained a reliable marker of mucosal healing across all disease extents, with area under the receiver-operating characteristic curve ranging from 0.878 to 0.915, and no significant differences between the extent categories (DeLong test, P ≥ 0.2919).

FC showed a significant association with disease extent yet remained a reliable surrogate marker for mucosal healing across all disease extents.