How IBS Is Diagnosed & FODMAP Tests

Getting a diagnosis of a chronic medical condition can be a challenging process! Understanding what symptoms the doctors are looking for and what medical tests are available, is the first step in getting a diagnosis for irritable bowel syndrome (IBS).

Irritable bowel syndrome can be diagnosed using a combination of the Rome IV criteria, and through ruling out other gastrointestinal disorders.

What are the Rome IV Criteria?

The Rome IV is a set of criteria that most IBS patients have in common. According to IBS experts, the Rome criteria are considered to be 98% accurate at identifying patients with IBS (1)

The criteria are:

Recurrent abdominal pain, on average, at least 1 day per week in the last 3 months, associated with 2 or more of the following criteria:

1. Related to defecation
2. Associated with a change in frequency of stool
3. Associated with a change in form (appearance) of stool

Criteria fulfilled for the last 3 months with symptom onset at least 6 months before diagnosis.

(2)

If you have been presenting with abdominal pain, bloating, and change in bowel habit then your doctor will decide if you match the Rome IV Criteria listed above and then will discuss red flag symptoms.

What are red flag symptoms?

Red flag symptoms indicate that there could be other serious medical conditions that need to be ruled out before diagnosing you with IBS (3 4). Additional medical tests will be used to rule out other medical conditions linked to red flag symptoms.

Red flag symptoms include:

• unintentional and unexplained weight loss
• rectal bleeding
• a family history of bowel or ovarian cancer, inflammatory bowel disease, coeliac disease
• onset of symptoms in patients aged greater than 50 years (over 60 years in the NICE guideline)
• nocturnal symptoms, e.g. waking from sleep with pain or the need to defecate
• anemia
• abdominal masses
• rectal masses
• inflammatory markers for inflammatory bowel disease.

(3; 4)

What other symptoms do the doctors look for?

To be diagnosed with IBS your abdominal pain and discomfort needs to be related to defecation or associated with altered bowel frequency, or stool form (4).

You should also have at least two to four of the following symptoms:

• abdominal bloating (more common in women than men), distension, tension or hardness
• altered stool passage (straining, urgency, incomplete evacuation)
• symptoms made worse by eating
• passage of mucus
• feeling of incomplete emptying

(3; 4)

You may also experience symptoms that include lethargy, nausea, backache and bladder symptoms, as these are also common in people with IBS (4).

What medical tests are used to help diagnose IBS?

If your doctor believes you meet IBS diagnostic criteria, he/she may deem it appropriate to run the following tests to rule out other diagnoses:

• full blood count (FBC)
• erythrocyte (red blood cell) sedimentation rate (ESR) or plasma viscosity
• c‑reactive protein (CRP)
• antibody testing for coeliac disease (endomysial antibodies [EMA] or tissue transglutaminase [TTG]).

(3; 4)

What medical tests are generally not necessary when being diagnosed with IBS?

Unless you have red flag symptoms, there is often no need to put you through additional medical tests, such as:

• ultrasound
• rigid/flexible sigmoidoscopy
• colonoscopy; barium enema
• thyroid function test
• faecal ova and parasite test
• faecal occult blood
• hydrogen breath test (for lactose intolerance and bacterial overgrowth).

(4)

If your doctor is concerned he/she will refer you on to see a gastroenterologist. A gastroenterologist is a physician who has specialised training and unique experience in the management of diseases of the gastrointestinal tract and liver (5).

Are there any tests that help diagnose intolerance to certain FODMAP groups?

If you have been diagnosed with Irritable Bowel Syndrome (IBS), your medical practitioner can then tell you if trialing the low FODMAP diet is the right solution for you.

If the low FODMAP diet is recommended, they will place you on a strict low FODMAP diet for 2 to 6 weeks (6 7). A dietitian will then review your progress and help you test the different FODMAP groups (6 7). Your dietitian can then advise you on which foods and how much you can re-introduce into your diet. This method is the most effective way to test your tolerance levels to all of the FODMAP groups.

Sometimes, breath tests will be performed in a hospital to identify if you malabsorb lactose, fructose, or sorbitol. The test works by measuring the amount of gas (hydrogen and/or methane) in your breath after consuming one of the FODMAP sugars (6 7). If there is a significant rise in one or both of these gases then it can be confirmed that you malabsorb that particular FODMAP sugar (6 7).

However, latest breath test research highlights that these test results may be inaccurate:

Since writing this article further research has shown that hydrogen breath testing is not an accurate way of diagnosing FODMAP intolerances (8 9 10). These tests can show both false positive or negative results, which means a positive breath test may not mean you will have issues digesting the sugar (9). Additionally, the sugar dosages used in the breath tests are well above the standard amount that would be consumed in your average meal (9). Large amounts of these sugars can trigger symptoms even in people who do not normally experience gastrointestinal issues. The most reliable way to diagnose which FODMAP groups you malabsorb is through a strict elimination diet with the guidance of a FODMAP trained dietitian.

You can read more about hydrogen breath tests here. 

Are there other food intolerance tests that can be used?

Your doctor might use IgE blood test, skin prick test or other food challenges to check if you have a food allergy (11). A food allergy is where you have an immune system response to consuming certain foods (11). These tests are unlikely to show if you have food intolerances (this is where your body reacts to a certain food but it is not related to an immune system response).

Are there any tests that should be avoided when diagnosing food intolerances?

Many food intolerance tests on the market lack sufficient scientific evidence and are not good diagnostic tools for diagnosing food intolerances.

Here are some of the tests that are not recommended by medical professionals:

IgG blood tests (IgG4, York Test, IgG RAST/ELISA Testing). These blood tests look at IgG antibodies present in the blood, and test results claim that if there is an increase in IgG antibodies to a certain food then that indicates a food intolerance (11 12 13). There is no strong evidence supporting this theory (11 12).

Kinesiology is based on the belief that when you are intolerant to a food it creates an energy imbalance, which can be identified through muscle testing (11). There is no strong evidence supporting this theory (11 12).

Hair analysis/testing is when hair is sent to the laboratory and energy fields are scanned to look for imbalances (11). This is an unproven method of allergy and food intolerance testing and has no scientific basis (11 12).

Electrodermal (Vega) test measure the electromagnetic conductivity in the body with the belief that if you are intolerant to a food it will cause a dip in the electromagnetic conductivity (11). Research studies show that this test is not scientifically valid (11 12).

Final Thoughts

Please talk to your doctor if you are concerned that you have IBS. Your doctor will be able to determine if it is IBS or another medical condition, that is contributing to your symptoms. You and your doctor can then discuss treatment options and food intolerance testing to help you manage your symptoms.