For acute severe colitis (ASC) patients, corticosteroids (CS) was recommended as the first-line treatment in the guideline, but patients have a great risk of requiring colectomy or turning to second-line treatment. This study aim to verify the effectiveness of ulcerative colitis endoscopic index of severity(UCEIS) in predicting the reaction to corticosteroids, and explores the possibility that noninvasive marker fecal calprotectin (FC) could act as an alternative to UCEIS.

Inclusion Criteria:

1. Patients with a confirmed diagnosis of ASC according to Truelove and Witt's criteria;
2. Patients were generally able to tolerate the flexible colonoscopy before start of CS treatment;

Exclusion Criteria:

1. Patients with incomplete colonoscopy, inadequate fecal sample;
2. Patients with indeterminate diagnosis of ASC (colorectal cancer, Crohn's disease) according to colonoscopy;
3. Patients with infectious colitis, Clostridium difficile and CMV infection, primary immunodeficiency, recent history of immunosuppressant within 3 months.
4. Patients with bowel resection, intestinal anastomotic, and ileum enterostomy.