Irritable bowel syndrome is commonly diagnosed based on symptoms. Patients are often asked to maintain a symptom diary. Based on the frequency and severity of the symptoms diagnosis is usually made.

There are no specific tests for diagnosis of IBS. Tests are ordered only to exclude other conditions of the gastrointestinal tract like cancers, inflammatory bowel disease, Celiac disease etc. that may have similar symptoms as IBS. (1)

Diagnosis begins with taking complete medical history with detailed description of symptoms and a detailed physical examination. Tests like routine blood tests, stool examination tests, X rays, abdominal ultrasound examination and others are conducted to exclude other diagnosis. (1, 2, 3, 4)

Colonoscopy

In many cases a sigmoidoscopy or colonoscopy is suggested. This is especially true in patients who present over the age of 50.

This involves passage of a thin, flexible tube with a camera on the front tip via the anus. The camera sends images of the inside of the colon and intestine to the doctor.

The images can help detect colon disease like cancers and inflammatory bowel diseases like Ulcerative Colitis and Crohn’s disease.

Lactose intolerance

Sometimes Lactose intolerance test may be needed in patients who have worsening of symptoms on milk or milk product intake.

Lactase is an enzyme needed to digest the sugar (lactose) found in dairy products. If a person is deficient of this enzyme they tend to develop abdominal pain, gas or bloating and diarrhoea similar to IBS.

The prevalence of lactose intolerance in patients with IBS is about 25%, which is not significantly higher than the general population and this lactose intolerance is not implicated as a cause of IBS. Stool is examined for blood, parasitic or bacterial infections as well.

Diagnosis of IBS

Once the tests come up negative the symptoms of IBS are scored to make the diagnosis.

Specific parameters like duration, frequency and intensity of pain, triggers of bowel movement changes, specifics of bowel movement and stool appearance changes are looked at in details. (1, 2)

The criteria for diagnosis includes several standards, the most popularly used of which is the Rome criteria, for IBS and other functional gastrointestinal disorders.

Functional gastrointestinal disorders are those in which tests and imaging studies show normal bowels but the functions of the bowel are not so. (3, 4)

Pattern of symptoms

Symptoms must be in a pattern before diagnosis is made. This includes –

• Abdomen pain and discomfort for at least 12 consecutive or non-consecutive weeks
• Relief with defecation
• Onset associated with change in frequency of bowel movements
• Onset associated with change in nature and consistency of stool
• At least two symptoms such as change in the frequency or consistency of stools, urgency for bowel evacuation but incomplete evacuation, mucus passage in stools, bloating and gaseous distension of the abdomen.
• Symptoms of stool frequency more than thrice daily or less than thrice weekly may be one of the less important symptoms. Abnormal stool consistency (loose or hard) in at least 25% of all defecations, abnormal symptoms (urgency, straining and incomplete evacuation) in 25% of all defecations, passage of mucus in 25% of all defecations and bloating on 25% or more days are also less important symptoms.
• If there are symptoms of weight loss, fever, rectal or anal bleeding, nausea and continuous vomiting, severe pain and uncontrolled diarrhoea in patients over 50 other diagnoses should be ruled out.

The Manning Criteria of IBS

The Manning Criteria is another set of guidelines that determine the diagnosis of IBS.

Manning criteria include six symptoms –

1. Relief of abdominal pain after passage of stool
2. Bloating
3. Incomplete evacuation
4. Loose stool with pain
5. Passage of mucus
6. More frequent bowel motions