How do doctors diagnose IBS?

If you’re currently struggling with gut issues such as abdominal pain, bloating, gas, constipation or diarrhea, chances are that you may have come across IBS, also known as Irritable Bowel Syndrome as a possible diagnosis.

You may have also received a diagnosis of IBS already.

But either way, if you have severe IBS symptoms, it’s not uncommon to worry that there is something more serious happening because of the level of pain and discomfort you’re in.

In this case, either you, your doctor, or both of you will want to have additional tests carried out to check what’s happening in your gut. So what are these tests? And how do doctors use them to diagnose IBS?

In this post I’m going to take you through 5 of the most common tests that your doctor might recommend to help diagnose your gut issues.

Getting a diagnosis of IBS (Irritable Bowel Syndrome) can be a long and frustrating journey. I hope to help you understand the most common tests, their uses, and how they diagnose IBS.

(To explore more videos on IBS and digestive health, head on over to The Calm and Happy Gut YouTube channel).

How is IBS diagnosed?

Unfortunately, there is no specific test for IBS; it is diagnosed based on your symptoms.

The criteria for a positive IBS diagnosis include experiencing abdominal pain related to having a bowel movement. There should also be a change in stool frequency and consistency for at least three months.

This criteria is part of something called the Rome Criteria and we are up to Version IV.

Doctors diagnose IBS based on your symptoms and exclude other conditions using diagnostic tests and your personal background.

Now in most cases, a diagnosis of IBS can be made without additional tests. However if your symptoms include anaemia, bleeding from your bottom or blood in your stool, a fever, significant weight loss, or the sudden onset of symptoms after the age of 40, then testing would usually be indicated.

So let’s go through the 5 tests which your doctor might request and why.

1. Blood Test

A fairly likely scenario is that your doctor will start with a blood test to check for low iron levels and also inflammatory markers in the body. Now a blood test is fairly low invasive and can help reveal a number of things.

For example, low iron can point to anemia and can also point to internal bleeding which can occur with Inflammatory Bowel Disease, also known as IBD. Raised inflammatory markers in your blood may also signal that your symptoms may be due to an inflammatory disease.

For more on the differences between IBS and IBD, make sure you check out this post here.

2. Stool Analysis

A stool analysis can check for both blood in your stool (another sign of Inflammatory Bowel Disease) and it can also check for signs of infection and parasites.

Your doctor will be looking for different things depending on your own personal symptoms and background, but a stool analysis can help to rule out other gut disorders. It’s also a very low invasive way to get a clearer look at what is going on.

3. A Sigmoidoscopy

Doctors use a Sigmoidoscopy, a thin flexible instrument inserted into your rectum, to examine your sigmoid colon.

This is the final 40 centimetres or so before it reaches your rectum, and is the final part of your digestive system and connects your large intestine to your anus.

Why would your doctor refer you for this test?

Well, your doctor or specialist uses a Sigmoidoscopy to rule out structural or infectious diseases; it’s also less invasive than a colonoscopy, which I’ll cover shortly.

4. A barium enema

If you are over the age of 40 or have a family history of colon cancer or polyps, your doctor may recommend this test.

Now, I understand it might sound ominous, so let me clarify what it is and its purpose.

A barium enema is a test that highlights your large bowel, including the colon and rectum, for clearer visibility on an X-ray. This is because, unlike X-rays for other body parts, preliminary preparation is necessary to visualize your digestive tract.

During this test, a white liquid called barium is passed into your bowel through your bottom, and this test is usually carried out at a hospital radiology department by a radiologist or radiographer.

Nowadays, doctors prefer alternative tests like colonoscopies over barium enemas, which are less common.

But a barium enema can sometimes be a useful way of finding the cause of problems like blood in your stools or a constant change in your bowel habits.

5. A colonoscopy

A colonoscopy is a test to check the inside of your bowels.

Since it’s a quite invasive test, doctors generally recommend it only if they consider your symptoms as red flags or if your personal history requires further investigation.

As I mentioned at the start of this post, doctors generally don’t require these tests for diagnosing IBS. However, if your doctor refers you for a colonoscopy, they seek more information about what’s happening inside.

So what is this test?

During a colonoscopy a  long, thin, flexible tube with a small camera inside it is passed into your bottom and up into your bowel. 

Now despite its invasive nature, a colonoscopy is very helpful, because it can look for a number of things:

  1. Firstly, it can help to identify the cause of your bowel symptoms. For example, if you are experiencing bleeding from your bottom/finding blood in your stool, suffering with ongoing diarrhea or constipation that does not go away. Or if you are losing weight or feeling really tired for no reason.
  2. Secondly, a colonoscopy can be used to check for growths inside of your bowel such as polyps or if there is a suspicion of cancer, and;
  3. Thirdly, a colonoscopy can be used to look for signs of other bowel conditions such as Crohn’s disease, diverticular disease or diverticulitis, ulcerative colitis, and bowel cancer.

In summary

Now with all the tests, what your doctor recommends for you is going to be 100% based on your personal situation. So the information I can give to is general in nature and should not be used to diagnose.

If you’re tired of IBS symptoms and unsure where to turn, you’re in the right place for help.

Here’s how I can help you with your IBS:


Work with me 1:1 online and finally take back control of your IBS using gut directed hypnotherapy and Cognitive Behavioural Therapy (CBT). Working together over 6 sessions I’ll help you restore regular gut function, relieve pain and discomfort, and you enjoy life again. With a personalised, supportive and caring approach, The Calm Gut Program is evidence based and backed by science. Learn more here.


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Discover what’s really causing your IBS flare ups, and how to calm your gut naturally. (Chances are that not even your doctor has told you about these). Get your FREE copy here.

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