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Irritable Bowel Syndrome (IBS): Diagnosis

Last updated on September 12, 2021

Irritable Bowel Syndrome (IBS): DiagnosisIt is estimated that the typical patient visits an average of three different physicians over a three-year span before receiving the diagnosis of irritable bowel syndrome (IBS). Because there is an absence of distinguishing physical or laboratory markers in IBS, the diagnosis is based on patient symptoms. The diagnosis must be confirmed by the exclusion of other conditions, such as malabsorptive disorders, metabolic disorders, dietary factors, infection, inflammatory bowel disease, psychological disorders, or gynecological disorders.

The diagnostic criteria for irritable bowel syndrome (IBS), known as the ROME II criteria (Table 1), were recently updated by the International Working Party, a multinational panel of gastroenterologists. The ROME II criteria require patients to report abdominal pain for at least twelve weeks (consecutive or nonconsecutive) of the year that has two of three characteristics: 1) relieved upon defecation, 2) associated with a change in stool frequency, and/or 3) associated with a change in stool form. The criteria, intended for use in combination with a thorough patient history, physical examination, and laboratory evaluation, also provide the clinician with a list of common symptoms that support a diagnosis of irritable bowel syndrome (IBS).

Table 1:

ROME II Criteria for the Diagnosis of IBS
Abdominal pain for 12 weeks or more in the last 12 months with two or more of the following features:

  • Relieved with defecation
  • Onset associated with a change in frequency of stool; and/or
  • Onset associated with change in form (appearance) of stool The following symptoms may be used to support the diagnosis:
  • Less than three bowel movements per week
  • More than three bowel movements per day
  • Hard or lumpy stools
  • Loose or watery stools
  • Straining during a bowel movement
  • Urgency (having to rush to have a bowel movement)
  • Feeling of incomplete bowel movement
  • Passing mucus during a bowel movement
  • Abdominal fullness, bloating, or swelling

Diarrhea-predominant: one or more of symptoms 2, 4, or 6 and none of symptoms 1, 3, or 5

Constipation-predominant: one or more of symptoms 1, 3, or 5 and none of symptoms 2, 4, or 6

Detailed information regarding the nature, severity, location, and timing of symptoms is gathered during the patient history. Medications that can precipitate IBS-like symptoms, such as anticholinergic agents or antibiotics (Table 2), may be identified. Certain food products can be an exacerbating factor in the disorder and exclusion of caffeine, alcohol, chocolate, and dairy products (Table 3) may be necessary.

The physical exam in an irritable bowel syndrome (IBS) patient will typically be normal except for mild abdominal tenderness. Laboratory testing is based upon predominant symptoms and may include a complete blood count, erythrocyte sedimentation rate, C-reactive protein, thyroid and liver function tests, and a stool evaluation and culture. Clinical features that are not consistent with IBS and necessitate further work-up or referral include onset of symptoms after age 50, nocturnal symptoms, and warning signs of other diseases (Table 4).

Table 2:

Medications That Can Affect Bowel Habits
Type of Medication Example(s) Potential Effect(s)
Antacids Magnesium Diarrhea
Antacids Calcium, aluminum Constipation
Analgesics Opioids, nonsteroidal anti-inflammatories Constipation
Antibiotics All classes, especially broad spectrum Diarrhea
Anticholinergics Benztropine Constipation
Anticonvulsants Carbamazepine Constipation
Antihypertensives ACE inhibitors, beta-blockers Constipation
Antilipemic agents Gemfibrozil, probucol Diarrhea
Antimotility agents Loperamide Constipation
Calcium channel blockers Verapamil Constipation
Cardiac agents Quinidine, digoxin Diarrhea
Diuretics Thiazides Constipation
Hematinics Iron Constipation
Prokinetic drugs Cisapride, metoclopramide Diarrhea
Prostaglandins Misoprostol Diarrhea
Psychotherapeutics Phenothiazines, butyrophenones Constipation
SSRIs Citalopram, paroxetine, fluoxetine Diarrhea/constipation
Tricyclic antidepressants Amitriptyline, nortriptyline Constipation
Vinca alkaloids Vincristine Constipation

Table 3:

Food or Drink That Can Exacerbate IBS
Apple or grape juice
Carbonated beverages
Dairy products
High-fat foods

Table 4:

Warning Signs Not Attributable to IBS
Abnormal laboratory resultsAnemia

Bloody or black, tarry stools


Frequent nocturnal symptoms

Onset of symptoms in patient over age 50

Persistent diarrhea or severe constipation

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