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For further information, see CMDT Part 15-33: Irritable Bowel Syndrome

Key Features

Essentials of Diagnosis

  • Common chronic functional disorder characterized by abdominal pain with alterations in bowel habits

  • Symptoms usually begin in late teens to early twenties

  • Limited evaluation is intended to exclude organic causes of symptoms

General Considerations

  • No definitive diagnostic study

  • Idiopathic clinical entity characterized by chronic (> 3 months) abdominal pain or discomfort that occurs in association with altered bowel habits that may be continuous or intermittent

  • Abdominal discomfort or pain that has two of the following three features

    • Related to defecation

    • Associated with a change in frequency of stool

    • Associated with a change in appearance of stool (lumpy or hard; loose or watery)

  • Other symptoms include

    • Abnormal stool passage (straining, urgency, or feeling of incomplete evacuation)

    • Abdominal bloating or feeling of abdominal distention

    • Other somatic or psychological complaints


  • Up to 10% of the adult population have symptoms compatible with irritable bowel syndrome, but most never seek medical attention

  • Approximately two-thirds of diagnosed patients are women

Clinical Findings

Symptoms and Signs

  • Subjective abdominal distention; visible distention not clinically evident

  • Abdominal pain, intermittent, crampy, in the lower abdomen, that may be improved or worsened by defecation

  • More frequent or less frequent stools with the onset of abdominal pain

  • Looser stools or harder stools with the onset of pain

  • Constipation, diarrhea, or alternating constipation and diarrhea

  • Physical examination usually is normal

  • Abdominal tenderness in the lower abdomen is common, but not pronounced

  • Bloating, flatulence, and diarrhea may be exacerbated in some patients who eat poorly absorbed, fermentable, monosaccharides and short-chain carbohydrates ("FODMAPS")

Differential Diagnosis

  • Inflammatory bowel disease

  • Colonic neoplasia

  • Celiac disease, bacterial overgrowth, lactase deficiency

  • Gynecologic disorders (endometriosis, ovarian cancer)

  • Depression and anxiety

  • Sexual and physical abuse

  • Small bowel bacterial overgrowth (possibly in up to 65% of irritable bowel syndrome patients)


Physical examination

  • Digital rectal examination should be performed in patients with constipation to screen for paradoxical anal squeezing during attempted straining that may suggest pelvic floor dyssynergia

  • A pelvic examination is recommended for postmenopausal women with recent onset constipation and lower abdominal pain to screen for gynecologic malignancy

Laboratory Tests

  • Complete blood count, erythrocyte sedimentation rate, C-reactive protein

  • Serum electrolytes, creatinine, albumin, liver chemistry tests

  • Fecal occult blood or fecal immunochemical test

  • Thyroid function tests

  • Celiac disease serology (IgA tissue transglutaminase [tTG] antibody)

  • Stool examination for ova and parasites if diarrhea

  • D-[14C]xylose, glucose or lactulose breath tests to screen for small bowel bacterial overgrowth

Imaging Studies

  • Colonoscopy or air-contrast barium enema for patients ...

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