Fecal Calprotectin Levels in Post-Metabolic Bariatric Surgery Patients: A Retrospective Study.

Introduction: Fecal calprotectin (FCP) is a key biomarker for gastrointestinal inflammation, aiding in differentiating irritable bowel syndrome from active inflammatory bowel disease (IBD). Metabolic bariatric surgeries (MBSs), such as Roux-en-Y gastric bypass or sleeve gastrectomy, alter gastrointestinal physiology, potentially affecting the applicability of standard FCP cutoff values in this population. Methods: This retrospective study included 340 patients who underwent MBS and subsequent FCP testing between January 2000 and June 2024. Patients with preoperative IBD were excluded. The primary outcome was to identify the optimal FCP cutoff values for relevant colonoscopy findings. Secondary outcomes included median FCP levels, colonoscopy results, and subgroup analyses based on sex, surgery type, and time to gastrointestinal evaluation. Results: The median FCP level across all patients was 51 µg/g (IQR 30-82). Among 124 patients undergoing colonoscopy, the median FCP was 61 µg/g (IQR 34-104). There was no significant difference between patients with (69.5 µg/g, n = 50) or without (59 µg/g, n = 74) relevant findings, including malignancy or IBD (p = 0.101). No significant differences in FCP levels were observed between subgroups based on cholecystectomy status, biliopancreatic limb length, types of surgery, body mass index, time to presentation since MBS, or proton pump inhibitor use. ROC analysis identified an optimal cut off of 59.5 µg/g (sensitivity: 64.6%; specificity: 63.4%; area under the curve: 0.653; Youden's index 0.280). Conclusion: In patients following MBS, the optimal FCP cutoff value would be at 59.5 µg/g. However, given the low Youden's index and the minimal difference compared to the standard cutoff value of 50 µg/g, maintaining this standard, seems more practical in clinical settings.