Irritable Bowel Syndrome (IBS) Workup

Updated: Feb 15, 2022
  • Author: Jenifer K Lehrer, MD; Chief Editor: BS Anand, MD  more...
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Approach Considerations

A comprehensive history, physical examination, and tailored laboratory and radiographic studies can establish a diagnosis of irritable bowel syndrome in most patients. The specificity of the Rome III criteria may be improved by including information about nocturnal stools, somatization, and affective disorders on the basis of the clinical history as well as including hemoglobin and C-reactive protein levels with other diagnostic studies. [30] Routine serologic or genetic testing is not indicated in patients with irritable bowel syndrome (IBS) in all US populations as it appears that celiac disease is uncommon in IBS in this country. [31]

The 2009 American College of Gastroenterologists (ACG) evidence-based position statement on the management of IBS does not recommend laboratory testing or diagnostic imaging in patients younger than 50 years with typical IBS symptoms and without “alarm features”. Alarm features include the following symptoms and history [3] :

  • Weight loss

  • Iron deficiency anemia

  • Family history of certain organic GI illnesses (eg, inflammatory bowel disease, celiac sprue, colorectal cancer)

Although rectal bleeding and nocturnal symptoms have also been considered alarm features, they are not specific for organic disease. Patients with IBS-D or IBS-M should have serologic testing for celiac sprue. Patients aged 50 years and older should have more extensive testing, including a colonoscopy. [3]


Laboratory Studies

Blood studies

A complete blood cell (CBC) count with differential to screen for anemia, inflammation, and infection is indicated. A comprehensive metabolic panel to evaluate for metabolic disorders and to rule out dehydration/electrolyte abnormalities in patients with diarrhea is also indicated.

Stool examinations

Microbiologic studies to consider include the following stool examinations:

  • Ova and parasites (consider obtaining specimens for Giardia antigen as well)

  • Enteric pathogens

  • Leukocytes

  • Clostridium difficile toxin


History-Specific Examinations

Hydrogen breath testing to exclude bacterial overgrowth may be considered in patients with diarrhea to screen for lactose and/or fructose intolerance. Tissue transglutaminase antibody testing and small bowel biopsy are used especially in diarrhea-predominant irritable bowel syndrome to diagnose celiac disease.

Thyroid function tests are used to screen for hyperthyroidism or hypothyroidism. Serum calcium testing is used to screen for hyperparathyroidism.

Erythrocyte sedimentation rate and C-reactive protein measurement are nonspecific screening tests for inflammation.


History-Specific Imaging Studies

Gallbladder ultrasonography should be considered if the patient has recurrent dyspepsia or characteristic postprandial pain.

Abdominal computed tomography (CT) scanning is appropriate to screen for tumors, obstruction, and pancreatic disease if these are diagnostic possibilities.

CT and magnetic resonance (MR) enterography or wireless capsule endoscopy are employed if red flags exist to suggest enteritis (small bowel inflammation) or a tumor.

Colonoscopy is appropriate if alarm symptoms are present and in patients who otherwise qualify for screening colonoscopy.


Dietary Studies

Employ a lactose-free diet for 1 week in conjunction with lactase supplements. Improvement incriminates lactose intolerance, although the patient's clinical history and response to a trial may be unreliable. Therefore, some gastroenterologists recommend a formal hydrogen breath test. Fructose intolerance must also be considered.

Breath testing may also be used to evaluate for small intestinal bacterial overgrowth, as formal jejunal aspiration is rarely performed anymore.

Other dietary intolerances include FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols), gluten, and fructose. Low FODMAP diets can be helpful in this situation, though may be found very restrictive.


History-Specific Procedures

Anal manometry may reveal a spastic response to rectal distention or other problems. For many patients with irritable bowel syndrome, endoscopy appropriately includes flexible sigmoidoscopy to assess for inflammation or distal obstruction.

Esophagogastroduodenoscopy with possible biopsy is indicated in patients with persistent dyspepsia, if weight loss or symptoms suggest malabsorption, or if celiac disease is a concern. Colonoscopy is indicated for patients with warning signs, such as bleeding; anemia; chronic diarrhea; older age; history of colon polyps; cancer in the patient or first-degree relatives; or constitutional symptoms, such as weight loss or anorexia. A screening colonoscopy should be performed according to published guidelines.