Inclusion and exclusion criteria of importance in irritable bowel syndrome trials.

Although numerous diseases may mimic or be confused with irritable bowel syndrome (IBS), a detailed and precise clinical history and a normal clinical examination usually lead to an accurate diagnosis of IBS. The presence of symptom criteria and the absence of warning signs must be established. Before entering a clinical trial, several routine tests are generally required: total blood count, erythrocyte sedimentation rate, biochemistry screen, stool culture and examination for occult blood, ova, and parasites, and a recent (<2 years) normal flexible sigmoidoscopy or colonoscopy with biopsy. Blood and stool tests are not necessary for the diagnosis of IBS but are important in the framework of controlled trials. Esophagogastroduodenoscopy, abdominal ultrasonography, and malabsorption tests are needed only in patients with atypical IBS or for phase II trials in certain subgroups of patients. Chronic diseases, drugs, and toxic agents that may mimic IBS symptoms or exacerbate the disorder must be excluded. Errors in patient inclusion will be minimized if the duration and severity of IBS symptoms before inclusion is sufficient and will have little effect on the result of the trial if the new drug is really effective and the study well randomized with a correct calculation of sample size.