['Calprotectin is a granulocyte neutrophil-predominant cytosolic protein. Fecal concentrations are elevated in intestinal inflammation and may predict relapse in quiescent inflammatory bowel disease. We aim to investigate fecal calprotectin (FC) as a biomarker in predicting the clinical course of acute severe ulcerative colitis (ASUC).', 'In 90 patients with ASUC requiring intensive in-patient medical therapy (January 2005-September 2007), we investigated the discriminant ability of FC to predict colectomy and corticosteroid and infliximab nonresponse. All patients received parenteral corticosteroids as first-line treatment; 21 (23.3%) were also treated with infliximab (5 mg/kg), after failure of corticosteroid therapy.', 'Of 90 patients, 31 (34.4%) required colectomy, including 11 (52.4%) of those treated with infliximab. Overall FC was high (1,020.0 microg/g interquartile range: 601.5-1,617.5). FC was significantly higher in patients requiring colectomy (1,200.0 vs. 887.0; P=0.04), with a trend toward significance when comparing corticosteroid nonresponders and responders (1,100.0 vs. 863.5; P=0.08), as well as between infliximab nonresponders and responders (1,795.0 vs. 920.5; P=0.06). Receiver-operator characteristic curve analysis yielded an area under the curve of 0.65 to predict colectomy (P=0.04), with a maximum likelihood ratio of 9.23, specificity 97.4%, and sensitivity 24.0% at a cutoff point of 1,922.5 microg/g. Kaplan-Meier analyses showed that using 1,922.5 microg/g over a median follow-up of 1.10 years, 87% of patients will need subsequent colectomy.'] Does fecal calprotectin predict the clinical course of acute severe ulcerative colitis?