Common Tests

Common Tests.png

Common Tests you may Encounter

Although IBS has its own criteria for diagnosis, your doctor may order other tests as the symptoms of IBS can be similar to, or overlap with, the symptoms of several other conditions. These tests can help rule out other possible causes of your symptoms such as cancer, celiac disease, parasites or an inflammatory bowel disease (especially Crohn’s disease or ulcerative colitis). Although IBS can be debilitating and have a profound effect on quality of life, it does not carry the same long-term health risks or the treatment options of some other digestive conditions. 

Breath Tests

Breath tests measure the production of certain gases produced by bacteria in the digestive system. When the gut bacteria produce gases, the gases are absorbed across the gut wall and will eventually be detected in the breath as you breathe out, where they can be measured. Lactulose or glucose are the sugars more commonly given before the breath test.

  • Hydrogen breath test – this test is mainly used to determine intolerance to fructose, or lactose. However, it is not always a reliable indicator of intolerance.

  • Hydrogen/methane breath test to investigate SIBO (see SIBO). Production of methane may indicate the presence of specific bacteria that are associated with constipation.


Stool tests

  • FOBT (fecal occult blood test) – this test detects the presence of blood in the stool. It is one of the tests used to detect early signs of bowel cancer. People can have blood in the stool due to other conditions such as haemorrhoids, inflammation or infection.

  • Calprotectin – calprotectin is mixed with the stool when there is inflammation in the bowel and may indicate that someone has an inflammatory bowel disease such as Crohn’s disease or Ulcerative Colitis.

  • Test for parasites, ova, bacteria, viruses – eg. Giardia or pinworms especially if you have been abroad or had a gut infection recently.

  • Test for bile acids  - bile acids are made in the liver and help to break down dietary fat. They pass through the small intestine where they are reabsorbed at the end. When reabsorption is disturbed, the excess bile can lead to diarrhoea.


Colonoscopy – carried out by a gastroenterologist. A thin tube with a camera on the end is inserted into the large intestine through the anus. This allows the doctor to view the lining of the large intestine for any diseased tissue such as unusual growths, or signs of inflammation or scarring.

Endoscopy – is sometimes carried out. A small tube with a camera on the end is inserted into the mouth and down the throat to view the esophagus, stomach and sometimes the upper part of the small intestine.

Small intestinal biopsy – this is the gold standard test for celiac disease.  In suspected celiac disease the endoscopy, described above also involves taking several small samples of the lining of the small intestine for examination.

It does require that a person be consuming gluten regularly to be confident of the accuracy of the test. See below for more information about gluten and testing.

Laparoscopy – females only – two very small incisions are made on the abdominal wall. A small camera is introduced into one hole to look at the ovaries and to check for endometriosis. The symptoms of endometriosis can be similar to IBS so making sure it is not the cause is important.

Ultrasound, barium studies, abdominal x-rays may be carried out to look for abnormalities in the gut such as evidence of inflammatory bowel disease or abnormal structures.

Blood tests

  • General blood test for nutritional markers such as iron, vitamin B12.

    • When nutritional markers are within the normal range it suggests that digestion and absorption are working well.

  • Thyroid function test

  • Tests for inflammatory markers

  • Tests for celiac screening

    • IgA-human tissue transglutaminsae

    • IgA-endomysial antibody

Either or both of these tests may be ordered.

Serum IgA test (this is just to check that you are able to make the IgA antibody as 3-5% of people with celiac disease are IgA deficient).

  • Genetic testing

Certain genes called HLA DQ4 and DQ8 have been found to be present in 98.7% of people with celiac disease. If you have removed gluten from your diet and are reluctant to reintroduce it, you may be able to start with this genetic test. If that comes back negative then you are very unlikely to have celiac disease, however, if it comes back positive, it is worth considering the celiac screen.

  • Small intestinal biopsy

This is considered the gold standard test for celiac disease. It is carried out as an outpatient under sedation. A small tube with a little camera on the end called an endoscope is fed through the mouth, down the esophagus into the stomach and into the upper small intestine. It allows the physician to view the small intestine and inspect it for inflammation or abnormalities. Several small biopsies are taken and will later be examined under a microscope for evidence of inflammation and damage to the structure of the intestinal lining.  

A Note on Gluten

In order for these tests to be accurate it is important to include gluten regularly in your diet prior to the test. This is usually at least two slices of bread every day for 2-8 weeks prior to the test. The 2-8 week parameter reflects different research studies and differing opinions. Always check with your doctor what they advise for the most accurate testing.

Why Have the Gluten Screen

Celiac disease is a serious condition and the only treatment is a completely gluten free diet that must be strictly adhered to for life. If a person with celiac disease consumes gluten, even foods contaminated with gluten, they will be at risk for malnutrition, bone loss, infertility, and in rarer cases, lymphoma and bowel cancer.

The diet is more expensive than a regular diet and a formal diagnosis provides some financial advantages, such as tax breaks for the extra costs incurred by the specialized diet. It is also burdensome as a diet and can affect quality of life. If you do not have celiac disease you can be more liberal with your diet and it won’t negatively impact your health over the long term putting you at risk of the associated complications.

The most common gluten containing grains, wheat, barley and rye, also contain other components such as fructans, lectins and proteases that can produce irritable bowel syndrome symptoms. If your gut feels better without these grains in your diet, it may or may not be related to the gluten. In addition, people often feel more alert, more energetic and healthier when they remove refined white flour products such as bread, cakes, muffins, and cookies from their diet, but this is often related to improved blood sugar balance and the replacement with foods of higher nutritional quality.

Jill Burns