Characterization of remission levels in patients with ulcerative colitis treated with 5-aminosalicylates: results of the cross-sectional CARUC-ASA study by the Belgian IBD Research and Development Group.

5-Aminosalicylic acid (5-ASA) remains the first-line therapy for mild-to-moderate ulcerative colitis (UC). Modern treatment goals extend beyond symptom control to include steroid-free remission, endoscopic healing, and biomarker normalization. Real-world evidence on 5-ASA's ability to achieve these targets is limited. This study assessed remission levels and associated factors in Belgian UC patients in clinical remission on 5-ASA. This cross-sectional, multicenter, phase 4 study included UC patients in clinical remission (PRO-2 ≤ 1, no rectal bleeding) treated with 5-ASA for ≥6 months. Patients receiving corticosteroids, immunomodulators, or advanced therapies were excluded. Outcomes were complete clinical remission (PRO-2 = 0, no urgency), endoscopic remission (MES ≤ 1, UCEIS ≤ 1), complete endoscopic remission (MES = 0), histological remission (Geboes 0-1), biological remission (fecal calprotectin <150 µg/g), and deep remission (clinical, endoscopic, and histological). Adherence was assessed using MARS-5. In total, 198 patients were enrolled (median age 50 years; 41% female). Treatment was oral 5-ASA only (n = 134, 68%), rectal only (n = 19, 9%), or combination (n = 45, 23%). Biological remission was observed in 78%, endoscopic remission in 87%, complete endoscopic remission in 70%, and histological remission in 80%. Deep remission occurred in 24%, limited by persistent urgency (63%). Adherence was high (median MARS-5: 24). Oral 5-ASA only was significantly associated with endoscopic remission (P < .001). In this real-world Belgian cohort, patients in clinical remission on 5-ASA achieved high rates of objective remission, while deep remission was low because of persistent urgency. These findings confirm 5-ASA's continued relevance in mild-to-moderate UC and highlight the importance of addressing residual symptoms despite mucosal healing.