Calprotectin levels in Crohn's perianal fistula scraping are associated with fistula outcomes after surgical closure

BACKGROUND AND AIMS: So far, there are no diagnostic tools to identify Crohn's disease (CD) patients at risk of failure or recurrence after perianal fistula closure surgery. This study aims to analyse if fistula scrapings calprotectin levels in CD patients undergoing surgical fistula closure can be predictive of postoperative outcomes. METHODS: In this prospective study, fistula scrapings were collected from 47 TOpCLASS 2a patients who underwent a surgical closure procedure with or without mesenchymal stem cell (MST) between November 2019 and February 2024. Scraping calprotectin was determined by ELISA. The primary outcome parameter was the correlation between scraping calprotectin levels and clinical fistula closure and radiological remission (MAGNIFI score ≤ 6). RESULTS: Eighteen patients underwent primary surgical closure and 29 patients underwent surgical closure with MST. Scraping calprotectin levels were significantly lower in the primary closure group when compared to MST (822 μg/g (IQR 134-3285) vs. 2698 μg/g (IQR 1042-6000), p = 0.041). After a median follow-up of 18 months (IQR 14-51), overall, 68% clinical closure with 40% radiological remission was seen. In the primary surgical closure group, scraping calprotectin levels were significantly lower in patients with clinical fistula closure (586 μg/g (IQR 84-1454) vs. 5855 μg/g (IQR 3291-6000), p = 0.003). In contrast, in the MST group no significant differences were found for clinical closure, whereas higher scraping calprotectin levels were found in patients who reached radiological remission (4827 μg/g(IQR 2698-6000) vs. 1967 μg/g (IQR 428-3937), p = 0.033). CONCLUSIONS: These results suggest that scraping calprotectin can be used to identify patients amenable for primary surgical closure and select patients most likely to need additional treatment like MST.