Diagnosing Irritable Bowel Syndrome with Constipation

Core Diagnostic Criteria

The American Gastroenterological Association recommends that IBS-C be diagnosed using the Rome II criteria, which requires at least 12 weeks of abdominal discomfort or pain with 2 of 3 features: relieved with defecation, onset associated with a change in frequency of stool, and/or onset associated with a change in form of stool, combined with hard/lumpy stools and fewer than 3 bowel movements per week 1
The diagnosis is symptom-based and positive, not a diagnosis of exclusion, as stated by the European Society of Gastroenterology 2, 3

A working diagnosis can be safely made in general practice based on typical symptoms meeting Rome criteria, normal physical examination, and absence of alarm features, according to the National Institute for Health and Care Excellence 2, 3
The diagnosis is more likely if the patient is female, aged <45 years, and has a symptom duration >2 years, as suggested by the American College of Gastroenterology 2, 3, 5

Red flags requiring further investigation include fever, weight loss, blood in stools, anemia, and nocturnal symptoms, as recommended by the American Gastroenterological Association 1, 2, 3, 4
Patients over age 50 years should undergo colonoscopy due to higher pretest probability of colorectal cancer, as advised by the European Society of Gastroenterology 1
Selective additional testing, such as sigmoidoscopy, thyroid function tests, and antiendomysial antibodies, may be performed if symptoms are atypical or patient is over 45, as suggested by the National Institute for Health and Care Excellence 2, 3

Once a functional diagnosis is established, the incidence of new non-functional diagnoses is extremely low, as stated by the European Society of Gastroenterology 4, 5
Psychological stress and psychosocial factors may exacerbate symptoms and should be identified, particularly history of major life stress, comorbid psychiatric disorders, and maladaptive coping style, as recommended by the American Psychiatric Association 1