Predictive Efficacy of Fecal Calprotectin Assay by Magnetic Particle Chemiluminescence for Mucosal Healing in Moderate-to-Severe Ulcerative Colitis Patients Undergoing Initial Biologic Therapy（PRECAL）

Ulcerative colitis (UC) is a chronic non-specific inflammatory bowel disease that mainly affects the rectum and colon. It is characterized by frequent relapse and protracted course. Its incidence has been rising rapidly, imposing a substantial economic burden on both patients and society. Biologic agents serve as key therapeutic options for UC and are widely used in the management of patients with moderate-to-severe disease. Mucosal healing (MH) is a core therapeutic goal for UC. Endoscopy is the primary modality to assess endoscopic MH, yet it is an invasive examination.

Fecal calprotectin (FC) is a specific biomarker for intestinal inflammation, which can accurately reflect the inflammatory status of the gut and acts as an ideal non-invasive biomarker for patients with UC. A large number of existing studies have demonstrated that FC is strongly correlated with clinical disease activity, endoscopic findings and histological parameters, highlighting its great value in disease assessment.

Magnetic particle chemiluminescence assay features high sensitivity, rapid detection, wide linear range, excellent precision and accuracy, as well as high degree of automation. It enables full-course monitoring of FC levels across mild, moderate and severe inflammatory stages as well as disease remission, providing evidence for evaluating therapeutic efficacy and optimizing treatment regimens. Hence, it is an optimal method for detecting FC concentrations.

This is a national prospective, multicenter, observational study. Eligible participants are patients aged 18 years or older with moderate-to-severe active UC, disease extent classified as Montreal E2 or E3, newly initiated biologic therapy, and a confirmed UC diagnosis of more than 3 months. The total follow-up duration is 30 to 32 weeks. During follow-up, stool samples are collected for FC measurement, along with clinical data and endoscopic results of the enrolled patients.

The study endpoints are defined as endoscopic mucosal healing, clinically confirmed inadequate response to the current biologic therapy (where continued treatment is unlikely to achieve mucosal healing, necessitating treatment switching or combined medication), or completion of the 30-32-week follow-up.

The primary objective is to determine the cutoff value and predictive performance of the early (Weeks 2-4) reduction in FC measured by magnetic particle chemiluminescence assay for predicting mucosal healing in moderate-to-severe UC patients receiving initial biologic therapy.

The secondary objectives are as follows:

1. To identify the cutoff value and predictive performance of the early (Weeks 2-4) FC reduction detected via magnetic particle chemiluminescence assay for predicting sustained clinical response in moderate-to-severe UC patients on initial biologic therapy;
2. To explore the cutoff value and predictive performance of the early (Weeks 2-4) FC reduction for predicting sustained endoscopic remission in the above patient population;
3. To analyze the dynamic correlation between FC levels measured by magnetic particle chemiluminescence assay and clinical disease activity;
4. To assess the correlation between FC levels and endoscopic disease activity;
5. To establish a predictive model for mucosal healing at Weeks 30-32 in UC patients by combining symptom scores, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), FC levels and their reduction ranges.