Functional bowel disorders (FBD) are a spectrum of chronic gastrointestinal (GI) disorders characterized by predominant symptoms or signs of abdominal pain bloating, distention, and/or bowel habit abnormalities, and the absence of obvious anatomic or physiologic abnormalities identiﬁed by routine diagnostic examinations, as deemed clinically appropriate. Irritable bowel syndrome (IBS) is one of the most commonly diagnosed functional bowel disorders (FBD). characterized by abdominal pain and bowel dysfunction, presenting as constipation, diarrhea, or alternating periods of both. Incidence rates of IBS are seldom calculated, and prevalence estimates fluctuate both between and within countries. A literature review by Sperber and colleagues suggests that a global prevalence rate could not be estimated owing to the heterogeneity of the studies. The pooled prevalence rate that the investigators cited for North America, Europe, Australia, and New Zealand was 8.1%. While IBS is not associated with increased mortality rates, it represents a significant burden on affected patients and society as a result of direct medical costs, lost productivity, and reduced health-related quality of life.

The development and persistence of IBS symptoms are understood to be multifactorial. Consequently, diagnosis and treatment are complicated clinical endeavors. IBS is diagnosed by symptom-based criteria, initially proposed by Manning and subsequently modified and quantified in the Rome I, II, and III criteria. However, the available literature suggests that symptom based diagnostic algorithms, although often used for clinical and research studies, have poor sensitivity. Although diagnostic algorithms can discriminate IBS from health or upper gastrointestinal tract conditions, studies do not provide convincing evidence that the criteria can discriminate IBS from organic disease of the colon. Therefore, in clinical practice, medical history should include evidence of organic disease (alarm symptoms) in addition to the main symptoms. Rectal bleeding, anemia, weight loss, fever, family history of colon cancer, and age above 50 years are considered the warning signs of severe gastrointestinal disease. Colonoscopy is the most direct way to rule out organic colonic diseases. It is an agreement that patients who meet Rome criteria on IBS with warning signs are strongly advised to perform colonoscopy to rule out severe colonic diseases such as inflammatory bowel disease (IBD) and colorectal cancer . The diagnostic sensitivity of symptom criteria on irritable bowel syndrome without colonoscopy is not more than 69.7% in patients with suspected irritable bowel syndrome lacking warning signs. There is no consensus so far on whether patients with suspected IBS lacking warning signs need colonoscopy or not. However, the value of alarm symptoms in discriminating organic disease from functional disorders remains uncertain and further research is needed, especially as alarm features are common.

In 2016, the Rome IV criteria was updated and published, in which IBS involved several changes. And there are currently few clinical studies based on Roman IV. This cross-sectional study was designed to evaluate the predictive value of alarm symptoms for IBS and organic bowel diseases and the difference in predictive value between different subtypes based on Roman IV.

Data collection：Basic information: name, gender, race, age, BMI index (height, weight), marital status ；Gastrointestinal symptoms: IBS-related symptoms，change in form of stool，duration and incidence of symptoms； Alarm Symptoms: Rectal bleeding (black stool, blood on toilet paper), anemia, weight loss, fever, nocturnal symptoms； Lifestyle habits: eating habits (spicy stimulation, dietary fiber), smoking, drinking, sleep quality, daily exercise time; Family history: colorectal cancer, inflammatory bowel disease, celiac disease, etc; Personal history: history of gastrointestinal infections, life emergency events; Test results: laboratory test results，colonoscopy results. The investigators obtained relevant information through consultation, telephone follow-up, questionnaire follow-up.Through endoscopy results to determine organic or functional diseases, benign or malignant, through contacts with the basic data, to determine the alarm symptoms. Further more, this study was proved by the ethical committee of second hospital of Xi'an jiaotong university.