Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder that affects 10% to 20% of people worldwide. A substantial proportion of visits to primary care physicians and to gastroenterologists for GI problems are for IBS. A confident diagnosis by a physician is the initial and crucial step in receiving a clear explanation, effective treatment, and feeling less anxiety about what is causing symptoms.

Medical opinion has changed regarding how to diagnose IBS. The older view emphasized that IBS should be regarded primarily as a “diagnosis of exclusion.” Diagnosis was made only after diagnostic testing, often extensive, to exclude many disorders that could possibly cause the symptoms.

The newer approach bases diagnosis on defined patterns of signs and symptoms and limited diagnostic testing.

Making the Diagnosis

IBS is a condition with well-defined clinical features, and specific diagnostic criteria. This understanding can reduce unneeded testing.

While diagnostic testing is useful in evaluating certain problems, a physician can generally diagnose IBS by:

Recognizing certain symptom details
Performing a physical examination
Undertaking limited diagnostic testing
In fact, the absence of certain “red flag” signs, such as blood in the stool or fever, provides confidence that diagnostic testing to rule out other conditions is not needed.

This simpler approach is accurate, less expensive, and less burdensome to patients and physicians alike. It permits proper attention toward treatment and management rather than the unneeded and expensive pursuit of other diagnoses.

Typical Symptoms

The most important first thing for you to share with your doctor is a clear description of your symptoms experienced. Symptom-based criteria for the diagnosis of IBS have been evolving since 1978, when research proved the usefulness of certain symptoms to distinguish IBS from structural diseases.

In 1990, a group of specialists from around the world developed the “Rome Criteria,” a classification system currently in use for all the functional GI disorders including IBS. These symptom-based criteria are modified at times as new knowledge comes to light, making diagnosis more precise. The latest revision is known as Rome III.

The essential feature of IBS is abdominal pain. The abdomen is located below your chest and above your hips. The hallmark of the diagnosis is that the abdominal pain is improved by a bowel movement and is associated with a change in bowel habit. This means that the frequency or consistency of stools – either diarrhea or constipation – changes when the pain occurs.

IBS can be subtyped into categories based on the main bowel habit: IBS with constipation (IBS-C), IBS with diarrhea (IBS-D), or mixed IBS (IBS-M). The symptoms occur over a long term, tend to come and go, and may even change over time within an individual.

The Rome III Diagnostic Criteria*

Recurrent abdominal pain or discomfort** at least 3 days per month in the last 3 months associated with 2 or more of the following:

1) Improvement with defecation
2) Onset associated with a change in frequency of stool
3) Onset associated with a change in form (appearance) of stool

* Criterion fulfilled for the last 3 months with symptom onset at least 6 months prior to diagnosis.

** “Discomfort” means an uncomfortable sensation not described as pain.

The Rome III criteria are reliable only when there is no abnormal intestinal anatomy or abnormality in the biochemical (metabolic) process that would explain the symptoms. In other words, results from a physical examination and any tests are negative. They appear normal.

The presence of certain red flags or “alarm signs” call for special consideration of other disorders before symptoms can be attributed to IBS. These signs include:

• Anemia and other abnormal blood tests
• New onset of symptoms at age 50 or older
• Blood in the stools
• Fever
• Night time symptoms that awake the individual
• Unintentional weight loss
• Change in the symptom quality (e.g., new and different pain)
• Recent use of antibiotics
• A family history of other GI diseases like inflammatory bowel disease, celiac disease, or colon cancer
  Notably, these signs are not automatically cause for alarm. A separate, benign problem is often found that explains them. For example, rectal bleeding may be caused by hemorrhoids, or IBS symptoms may worsen during menstrual periods.

In addition to pain and bowel dysfunction, some people with IBS suffer from other chronic functional symptoms or conditions. Each of them may require a directed diagnostic approach. These problems can include:

• Fibromyalgia (muscle aching)
• Headaches
• Dyspepsia (upper abdominal discomfort or pain)
• Chest pain
• Urinary or gynecological symptoms
• Insomnia
• Anxiety
• Depression
• Diagnostic Testing

An experienced physician’s judgement is most important in determining what tests are needed. Testing is individualized depending on factors such as family history, presence of stress factors, symptom features, and others.

The tests that are especially relevant to the evaluation of IBS symptoms may include:

Blood Tests – A complete blood count is often done to check for anemia and other abnormalities. .

Stool Tests – Most commonly these check for a bacterial infection, an intestinal parasite, or blood in the stool.

Sigmoidoscopy or Colonoscopy – Visual examinations of the rectum and a portion or all of the large bowel (colon) performed with a scope. Usually done when there are certain signs, such as rectal bleeding or unexplained weight loss, or as part of diagnostic screening for colon cancer after age 50.

Barium Enema – Examines the large bowel, after being coated with barium, performed by taking x-rays. This test has for the most part been replaced by colonoscopy. Women who are pregnant or unsure whether they are pregnant should tell their physician, as this test should not be done in such cases.

Psychological Tests – Questionnaires that detect anxiety, depression, or other psychological problems may be used to supplement the evaluation.

Miscellaneous Tests – Other tests may be done depending on specific aspects of an individual’s illness, especially atypical symptoms or alarm signs. However, many people do not require these other tests.

Miscellaneous Other Tests

Summary

A knowledgeable health care professional can diagnose IBS by careful review of the person’s symptoms, a physical examination, and selected diagnostic procedures that are often limited to a few basic tests. Such a diagnosis is quite secure. People confidently diagnosed by a physician seldom discover another cause for their symptoms, even after many years of follow-up. With a clear diagnosis, both patient and health care professional can work together on the most effective treatment and management of IBS.

© 2014 IFFGD

Adapted from IFFGD publication 163, Current Approach to the Diagnosis of Irritable Bowel Syndrome, by George F. Longstreth, MD and Douglas A. Drossman, MD