A number of different tests may be needed to diagnose Crohn's disease, as it has similar symptoms to several other conditions.
During your initial assessment, your GP will usually ask you about the pattern of your symptoms and check whether there may be any contributing causes, such as:
- recent travel – for example, you may have developed travellers' diarrhoea while travelling abroad
- whether you're taking any medication, including any over-the-counter medicines
- whether you have a family history of Crohn's disease
Your GP may also carry out a series of standard tests to assess your general state of health. For example, they may:
- check your pulse
- check your blood pressure
- measure your height and weight
- measure your temperature
- examine your abdomen (tummy)
Your GP may then arrange a series of blood tests. These can be used to assess:
- the levels of inflammation in your body
- whether you have an infection
- whether you're anaemic, which could suggest you're malnourished or losing blood from your bowel
You may be asked to provide a stool sample, which can be checked for blood and mucus. It can also be used to determine whether your symptoms are being caused by a parasitic infection such as roundworm, or other infections.
A faecal calprotectin test may be offered to adults who have recently developed symptoms such as abdominal pain, diarrhoea or constipation and are being considered for specialist treatment. This test helps clinicians to distinguish between irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD).
After you've provided a stool and blood sample, you'll probably be referred to a gastroenterologist (a specialist in conditions of the digestive system). They'll discuss the results with you and carry out the tests described below if they're necessary.
A colonoscopy is a test used to examine the inside of your colon. It involves inserting a long, flexible tube called an endoscope into your colon through your back passage (rectum).
The endoscope has a light and a camera on the end. The camera can be used to send images to a television screen. These show the level and extent of inflammation inside your colon.
The endoscope can also be fitted with surgical tools that can be used to take a number of small tissue samples from different sections of your digestive system. This is known as a biopsy. The procedure may feel uncomfortable, but it's not painful.
These tissue samples will be examined under a microscope for the cell changes known to occur in cases of Crohn's disease.
Wireless capsule endoscopy
A wireless capsule endoscopy is a new type of test that involves swallowing a small capsule (about the size of a large vitamin tablet). The capsule works its way down to your small intestines, where it transmits images to a recording device worn on a belt or in a small shoulder bag.
A few days after the test, the capsule passes out of your body in the stool. The capsule is disposable, so you don't have to worry about retrieving it from your stools.
As this is a relatively new test, availability may be limited. In some cases, MRE or CTE scans may be used instead of capsule endoscopy.
MRE and CTE scans
Scans called magnetic resonance enterography/enteroclysis (MRE) or computerised tomography enterography/enteroclysis (CTE) may be used to examine the small intestine in people with suspected Crohn's disease.
Before having these scans, you'll either need to drink a harmless liquid called a contrast agent (enterography), or contrast agent may be placed through a tube in your nose that leads to your small intestine (enteroclysis). These contrast agents allow your small intestine to show up more clearly during the scans.
During an MRE scan, magnetic fields and radio waves are used to produce detailed images of your small intestines. During CTE scans, several X-rays are taken and assembled by computer to create a detailed image.
These tests are increasingly used instead of a small bowel enema or small bowel follow-through, because they allow more detailed examination of the small intestine. MRE scans also avoid any exposure to X-ray radiation.
Small bowel enema or small bowel follow-through
A small bowel enema (SBE) and small bowel follow-through (SBFT) are two similar tests that have traditionally been used to examine the whole of the inside of the small intestine, usually at the point where it meets the colon. They're sometimes used because only about the last 20cm of the small intestine is usually seen during colonoscopy.
During an SBE/SBFT, a local anaesthetic spray is used to numb the inside of your nose and throat. A tube is passed down your nose and into your throat before being threaded into your small intestine. This can feel unpleasant at first, but most people find they get used to the sensation after a few minutes.
A harmless liquid called barium is passed down the tube. The barium coats the lining of your small intestines, so they show up clearly on X-ray. A series of X-ray images will then be taken. The images can often highlight the areas of narrowing and inflammation caused by Crohn's disease.
After the test, you'll be advised to drink plenty of fluid to help wash the barium out of your body. You may notice that your stools look white for the first few days after having an SBE or SBFT. This is perfectly normal and nothing to worry about.