Abstract Background Reliable non-invasive biomarkers are needed to identify patients with ulcerative proctitis (UP) at higher risk of relapse. Fecal calprotectin (FC) is widely used in ulcerative colitis, but its predictive value in isolated proctitis remains less established. We aimed to evaluate the efficacy of FC for predicting clinical relapse during 12 months of follow-up in a real-world UP cohort. Methods A multicenter, prospective, observational study was designed in patients ≥18 years old with UP (defined according ECCO guidelines) under maintenance treatment with mesalazine suppositories. We evaluated sociodemographic data and FC at month 6 and 12. Relapse was defined as partial Mayo ≥2. Correlations, ROC curve, and multivariable logistic regression were used to evaluate the predictive value of FC for relapse. Results A total of 186 consecutive patients (62% male, mean age 52± 12 years, mean disease duration 10.5 ± 12 years) with UP were including across 14 Spanish hospitals. During the 12 months follow-up, 29 (16%) patients experienced clinical relapse. Mean FC values were significantly higher in relapsing vs non-relapsing patients (632 ± 1349 µg/g vs 116 ± 224 µg/g, p 0.001, Figure 1). ROC curve analysis demonstrated an AUC of 0.64 (95% CI: 0.56–0.73). The optimal FC cut-off to predict relapse was 40 µg/g, yielding 70% sensitivity, 55% specificity, 23% PPV, and 91% NPV, indicating that low FC levels are strongly associated with maintained clinical remission. In multivariable logistic regression, FC ≥ 40 µg/g remained an independent predictor of clinical relapse (OR 1.9, 95 % CI 1.4–2.7, p = 0.001). Younger age was also associated with a higher risk of relapse (OR 0.95 per year, 95 % CI 0.91–0.99, p = 0.015). No significant differences were observed according to other variables including suppository brand or disease duration. Conclusion This large prospective multicenter cohort of patients with UP demonstrated that FC was an independent predictor of relapse. A cutoff of 40 µg/g, notably lower than typically applied thresholds, showed a high negative predictive value and reliably identified patients at low risk of clinical relapse. Conflict of interest: Ferreiro Iglesias, Rocio: RF-I has served as a speaker, or has received research or education funding from AbbVie, Takeda, MSD, Pfizer, Janssen, Adacyte, Ferring, Casen Recordati, Palex, Tillotts Pharma, Dr. Falk, Chiesi, Faes Farma, Alphasigma. Nieto-García, Laura: none De Castro Parga, Maria Luisa: I declare that I have acted as a speaker for Abbvie, Johnson & Johnson, Takeda, Tillots Pharma and Dr. Falk Pharma. I have received travel or conference attendance grants from Abbvie, Faes, Dr. Falk Pharma, Pfizer, Johnson & Johnson, Takeda, Tillots Pharma and Ferring. Pérez Galindo, Pablo: None. Hernandez Camba, Alejandro: I have served as a speaker or has received research or education funding or advisory fees from Lilly, Takeda, J and J, FAES Pharma, Falk, Abbvie, Adacyte Therapeutics, Tyllots, Ferring, Kern Pharma, Alfasigma and Chiesi. García, María José: Other: MJ García has received financial support for travelling and educational activities from Janssen, Pfizer, Abbvie, Takeda and Ferring. Calvo ñiguez, María: No conflicts of interest Rodríguez-Lago, Iago: Financial support for traveling and educational activities from or has served as an advisory board member for Abbvie, Adacyte, Alfasigma, Biogen, Chiesi, Faes Farma, Ferring, Fresenius Kabi, Galapagos, Johnson & Johnson, Eli Lilly, Mirum Pharmaceuticals, Merck, Pfizer, Roche, Takeda, and Tillotts Pharma. Research support from AbbVie. Supported by a research grant from Gobierno Vasco-Eusko Jaurlaritza (Grant No 2020111061 and 2023222006). Martí, Eva: No conflicts of interests Iriarte Rodriguez, Ainara: No conflicts of interests Pallarés-Manrique, Héctor: No conflicts of interest Dueñas, Carmen: No conflicts of interest Zabalza San Martín, Lucía: No conflicts of interest Ramirez de la Piscina Urraca, Patricia: No conflicts of interest Rodríguez Alonso, Lorena: No conflict of interest Bastón Rey, Iria: Personal Fees: Iria Bastón Rey has received financial support for travelling and educational activities from or has served as an advisory board member for Abbvie, Johnson & Johnson, Takeda, Pfizer, Alfasigma, Ferring, Faes Farma and Otsuka Pharmaceutical and Adacyte. Martínez-Cadilla, Jesús: Received honoraria from AbbVie, Takeda, and Pfizer for lectures, and support from AbbVie, Johnson & Johnson, Ferring España, and Faes Farma for congress attendance. Carpio Lopez, Daniel: No conflicts of interest Álvarez Cancelo, Ana: No conflicts of interest Porto Silva, María Del Sol: none Zabana, Yamile: Personal Fees: AbbVie, Adacyte Therapeutics, Alfa-Sigma, Amgen, Boehringer Ingelheim, Dr Falk Pharma, FAES Pharma, Fresenius Kabi, Ferring, Galapagos, Janssen-J & J, Kern Pharma, Lilly, MSD, Pfizer, Sanofi, Sandoz, Takeda, Tillots Pharma Non-financial Support: Shire, Otsuka, Almirall Barreiro-de Acosta, Manuel: MBA has been speaker, consultant and advisory member for or has received research funding from MSD, AbbVie, Janssen, Kern Pharma, Celltrion, Takeda, Alphasigma, Lilly, Pfizer, Sandoz, Biocon, Abivax, Fresenius, Faes Farma, Ferring, Tillots, Chiesi, Adacyte, Diasorin, Oncostellae and SunRock.
Iglesias et al. (Thu,) studied this question.