Risk Factors for Acute Hemorrhagic Rectal Ulcer Syndrome and Its Prognosis: A Density Case-Control Study

Figure 1

Study flow diagram depicting selection of cases and controls. 13,916 index colonoscopies out of 23,988 were performed in the patients older than 20 years of age in a tertiary medical center in Tokyo, Japan. Thirty-eight acute hemorrhagic rectal ulcer syndrome patients were diagnosed. From the same database of index colonoscopies, 123 patients without rectal ulcer were selected as a control group by risk set sampling.