Faecal calprotectin for the diagnosis of bowel inflammation in patients with rheumatologic diseases: what is new in the last 5 years (2020-2025)?

Objectives: This study updated the evidence (2020-2025) on the diagnostic and prognostic value of faecal calprotectin (FC) in rheumatologic diseases, focusing on spondyloarthritis (SpA), rheumatoid arthritis, and fibromyalgia syndrome. Methods: A systematic search of PubMed, Web of Science, and Cochrane databases (January 2020-August 2025) was performed. Eligible studies included adults with established rheumatologic diseases reporting FC levels and their associations with gastrointestinal symptoms, endoscopic or histologic inflammation, disease activity, or incident inflammatory bowel disease. Results: In SpA, a substantial proportion of patients exhibited elevated FC levels, ranging from ∼25% to 70% depending on study design and thresholds (typically 50-250 µg/g). Several studies demonstrated concordance between elevated FC and microscopic or macroscopic intestinal inflammation. FC was frequently associated with gastrointestinal symptoms and, in some cohorts, correlated with disease activity indices and inflammatory burden. Medication exposure emerged as a key confounder, with nonsteroidal anti-inflammatory drugs associated with higher FC levels and biologic therapies generally associated with lower values. In rheumatoid arthritis, evidence remains limited but suggests that FC may be elevated in early or active disease and decrease with treatment. In fibromyalgia, limited data indicate elevated FC in symptomatic subgroups, although specificity for inflammatory processes is uncertain. Conclusions: FC is a promising noninvasive biomarker for detecting subclinical intestinal inflammation in rheumatologic diseases, particularly SpA. However, heterogeneity in study design, thresholds, and confounding factors limits its clinical applicability.