How is IBS Diagnosed?

Jan 21, 2017 by


You can have me read this article to you instead of reading it yourself…

Or you can read it the old-fashioned way below…

It doesn’t do much good to talk about what IBS is and what symptoms it can cause if we don’t have a way of confirming whether or not someone has it, right?

Well, that’s not exactly true, but it is helpful to understand how this condition can be diagnosed, because a diagnosis is your clearest path to understand what is happening and how to deal with it.

Unfortunately, one of the most effective ways to diagnose IBS is to check and make sure that you don’t have any other conditions first.  So your doctor might want to check for other conditions in addition to evaluating you for IBS.  One of the concerns that he may specifically want to rule out is any damage to your intestines.  Damage can be caused by conditions like inflammatory bowel disease, or IBD (learn more about the difference between IBS and IBD here).  This means that you may have to undergo some of the tests that are used for those other conditions, such as upper endoscopy, colonoscopy, and barium studies.  You may also have your stool evaluated, and your blood drawn and tested.

I promise that the “Chelsey Take” below is quite different than what you have found elsewhere.  Hopefully this whole series has been worth your reading thus far!

Rome-III Criteria

The actual diagnosis of IBS is made through a review of your symptoms.  There is no specific test that will be run – no blood draw, no collection of stool, no camera into your GI tract.  Simply a discussion between you and your doctor regarding your symptoms.  While you may undergo some of those other tests, they are only used to rule out other possible issues that you might have.  The actual diagnosis of IBS is done through the use of the ROME-III criteria.


A diagnosis of IBS requires that you have at least two of the following symptoms:

  1. Symptoms are relieved by going to the bathroom
  2. Recognized changes were associated with a difference in stool frequency
  3. Recognized changes were associated with a difference in stool appearance

A doctor will also take your description of your symptoms into account and see if they are aligned with what he would expect with a case of IBS.  But every person experiences IBS in a different way, which is why these criteria seem so broad on first glance.  They must include all of the different ways that people can experience the condition.


In addition to diagnosing you with IBS, this discussion of symptoms will also allow the doctor to classify your type of IBS.  These include cases in which diarrhea is the most common (or only) symptom, those in which constipation is the most common (or only) symptom, and those in which symptoms of constipation and diarrhea mix together.  Their abbreviations make sense when you think of it that way.

IBS-D – Diarrhea dominates
IBS-C – Constipation dominates
IBS-M – Mixed constipation and diarrhea

Other Diagnoses

Carbohydrate (Sugar) Sensitivities

We are learning that a large number of IBS cases are caused by sensitivities to different ingredients, so your doctor may want to test you for some of these sensitivities.

Most people are familiar with lactose intolerance, and that is a good example of an ingredient sensitivity.  When a person is intolerant of lactose, he can end up with abdominal pain, diarrhea, and gas.  But that person could react poorly to certain forms of dairy and not others, which makes it a confusing problem to have at times.

Carbohydrates (sugars) are a complicated group of molecules, and our bodies process each type just a little bit differently.  So some people may be sensitive to one of these many groups of sugar molecules.  There are tests available that look for some of these specific sensitivities.  In these tests, you will be asked to drink a liquid form of that particular sugar, and then breathe into a monitor at different times.  This monitor will evaluate the molecules that you are breathing out, which allows the doctor to assess if you are processing that sugar properly.

Bacterial Overgrowth

I mentioned before that if bacteria move to a new location in the GI tract, they can disrupt the function of the intestine.  When bacteria move into the small intestine, this is called small intestinal bacterial overgrowth (SIBO), a topic that I will discuss more in an upcoming article.

And it turns out that we can test for this!  This will be a “breath test”, much like the carbohydrate sensitivity tests.  You will be asked to drink a specific liquid and then breathe into a monitor at different times.  The molecules that you breathe out allow the doctor to see if bacteria are located further up your GI tract than they should be.  If so, then this likely indicates a case of SIBO, which is treated differently than a standard case of IBS.

Interested in more information on IBS?

Next: How is IBS Treated?

Or refer back to the IBS Info Hub.


Trivia and Terminology:

ROME III Criteria is a guideline to diagnose IBS based on the symptoms that are being experienced

Many of the tests that someone with IBS will have completed are used to rule out other conditions, not to diagnose IBS itself


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