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Investigations and tests

You will probably only need to have a few of the investigations and tests listed below. However, IBD is an on-going condition, so some of the investigations and tests may need to be repeated from time to time, or extra tests may be needed.


Endoscopy is the general name for a type of test which allows a specialist doctor or nurse (an endoscopist) to look directly at the inside of the digestive system, using an endoscope.

There are several different types of endoscope, depending on which part of the body is being examined. But, in general, an endoscope is a long, very thin and usually flexible tube with a light and a video camera attached to the end of it. The endoscope can be inserted either through the mouth to look at the top part of the digestive system, or through the anus to look at the colon and rectum. The video camera relays images to a screen outside the body, and this allows the endoscopist to get a clear look at the part of the gut they are examining.The endoscopist may also take a biopsy using the endoscope. This is a small scraping of cells from the lining of the gut, which can then be examined under a microscope in order to give more information.The endoscopy staff will provide you with detailed instructions on how to prepare for your endoscopy, and should be able to answer any questions you may have.


A colonoscopy is an endoscopy of the colon (large intestine). Colonoscopies are often used to assess the extent and severity of UC and Crohn’s Colitis (Crohn’s in the colon). Regular or ‘surveillance’ colonoscopies may also be recommended to check for dysplasia (abnormal cell changes which can be an early sign of bowel cancer) in people with longstanding and extensive UC or Crohn’s.The endoscope used in a colonoscopy is sometimes known as a colonoscope. It is a narrow and very flexible tube, long enough to examine the whole of the colon, and, if necessary, the lower end of the small intestine as well. It is inserted through the anus. 

Sometimes a special dye is used to make it easier to see any changes to the colon lining (this technique is called Chromoendoscopy).The colon has to be completely clean for this examination, so you will be asked to avoid certain foods and to drink a special laxative the day before the investigation. You may also need to stop taking some of your medications – you will be given detailed instructions.You may be offered sedation for your colonoscopy, to make you feel sleepy and relaxed. People’s experiences of colonoscopies can vary. A colonoscopy should not be painful but may be uncomfortable. If you are particularly concerned or anxious, talk through your sedation options with the staff at the endoscopy unit. As with any sedation for an endoscopy, you will need someone to take you home, and should not drive for 24 hours after the sedation.


This is similar to a colonoscopy, but only examines the sigmoid colon (the lower part of the colon) and the rectum. If you have a flexible sigmoidoscopy, you will probably be asked to use an enema to empty the bowel before you go to the endoscopy unit or once you have arrived. This examination is usually done without sedation. As air is used to expand the colon you may feel some discomfort, but this should pass once the examination is finished. Sigmoidoscopy is most useful for IBD limited to the left side of the colon.


A proctoscope is a very short endoscope which is used to examine the anal canal and may carried out at a clinic appointment if required.  It is a useful way of checking for internal haemorrhoids (piles), fissures (tears) and fistulas (abnormal channels linking different parts of the bowel).

Capsule Endoscopy

For this investigation you will be asked to swallow a small capsule. The capsule contains a camera, which takes a series of photographs as it passes through the digestive system. These photos are sent to a small data recorder worn around the waist. The capsule is disposable and should pass out of the body naturally, in a bowel movement.Capsule endoscopy is really useful for detecting inflammation in the small bowel but it is not suitable for everyone, for example people with strictures (a narrow section of the intestine).


Abdominal X-rays

Ordinary or plain abdominal x-rays cannot show as much detail of the digestive system as some of the other imaging techniques. However, they may be used in an emergency, or in the initial diagnosis of suspected severe IBD.

DEXA (Dual Energy X-Ray Absorptiometry) Scans

DEXA scanners use low dose x-rays to measure bone density, usually in the spine or thigh bone. This is a painless test that takes about 20 minutes. It can show whether bone density is normal, or whether the bones have become thinner and weaker – the condition known as osteoporosis.

Commonly used scans

CT (Computerised Tomography) or CAT (Computerised Axial Tomography) Scans

A CT scanner is a special machine that uses a series of x-ray beams to build up a detailed picture of the body. The scanner looks like a giant ring doughnut, and you lie on a moveable bed which slowly passes through the centre. X-rays are taken at different angles, and the images produced are put together to produce two dimensional cross sections of the body. 

You may be given an injection of contrast dye through a drip, so that tissues such as the blood vessels around the gut will show more clearly. You might also be asked to drink a certain amount of contrast.

A CT scan of the colon is sometimes referred to as a colonography or a ‘virtual colonoscopy’.

MRI (Magnetic Resonance Imaging)

MRI scans are used to produce cross sectional images of the body. They are being increasingly used to investigate IBD because they avoid the use of  X-rays. Instead, they use strong magnetic fields and radio waves to create images of the inside of the body. The MRI scanner looks like a long tube or tunnel, and you will be asked to lie on a moveable table which slides slowly inside this tunnel. As for a CT scan, you may be given a contrast (dye) through a drip, or asked to drink a special liquid containing a contrast agent.

The MRI scan is noisy, so you may be provided with ear plugs, or perhaps music to listen to. It is important to lie very still during the scan to stop the images becoming blurred. The scan can take from thirty minutes to over an hour and a half. This means that some people may find it uncomfortable, especially if they suffer from claustrophobia (fear of enclosed spaces). However, for IBD investigations, because the abdomen is usually the area being examined, your head may not be completely inside the scanner for the duration of the test.

MRI has the advantage of not using x-rays, and is a good way of looking at soft tissues such as muscles and the gut, as well as organs such as the liver.

It is particularly effective in detecting fistulas (abnormal channels linking different parts of the bowel), and abscesses, and distinguishing between active inflammation and scarring. 

Because it uses magnets, MRI scans are not suitable for people with pacemakers or certain kinds of metal implants. You will be given detailed information about this before the day of your scan.


Ultrasound is another form of scan helpful in IBD. Ultrasound scans may be used to look for gall stones and kidney stones. They are also good at detecting collections of fluids and thickened and inflamed parts of the bowel wall. Ultrasound may also show up abscesses and fistulas (abnormal channels linking different parts of the bowel).

Ultrasound scanners work by using very high frequency sound waves to create an image. A handheld sensor is moved over the surface of the skin, and this sends out sound wave signals which ‘bounce off’ internal organs as an echo. The scanner then picks up the echoes and converts them into an image. Ultrasound is safer than x-rays and this type of scan is often used with pregnant women to track the growth of their unborn baby.

Other investigations

Examination Under Anaesthetic (EUA)

If you have perianal Crohn’s, you may be given an examination under anaesthetic. This is often used to investigate fistulas, and sometimes a special probe is used to trace out the route of the fistula.

Stool Tests

Fresh stool samples can be examined to check whether a flare-up of IBD-like symptoms is actually caused by an infection. This type of test is called a stool microscopy, culture and sensitivity test.

For example, tests may be carried out to look for infections such as Salmonella, Campylobacter, and Clostridium Difficile. If you have recently travelled abroad you may need additional tests.

Faecal calprotectin stool tests can also be used to detect an increased level of specific proteins in the stools, which can be a sign of active inflammation. Doctors are increasingly using this type of test to help with the initial diagnosis of IBD, and to monitor the disease and the progress of some treatments.

Blood Tests

There are several blood tests which are used to help support a diagnosis of IBD, or to monitor the effects of IBD or its treatment.

Some of the blood tests used most often in IBD are described below:

Full Blood Count (FBC)

An FBC counts and measures the levels of the three main types of blood cells (red cells, white cells, and platelets). The number of white blood cells can indicate if there is any inflammation or infection in the body. An increase in the number of platelets (small cells involved in blood clotting) can also be a sign of inflammation. By measuring the level of haemoglobin (a molecule in red blood cells which carries oxygen through the body), a FBC test can detect anaemia.

Some of the drugs given for IBD, such as azathioprine and mercaptopurine, can affect the bone marrow and reduce the levels of red and white blood cells and platelets. People on these drugs are usually given regular FBC tests to help monitor their blood cell levels.

Inflammatory Marker Tests

Inflammation can increase the levels of some types of proteins found in the blood. Blood tests such as C - Reactive Protein (CRP) and Erythrocyte Sedimentation Rate (ESR) can be used to detect inflammation by measuring the levels of these proteins or ‘inflammatory markers’.

Liver Function Tests (LFTs)

A liver function test or LFT can help to show whether the liver is working properly.  An LFT measures the levels of a specific group of proteins and enzymes found in the blood. LFTs usually also include a test for a protein called serum albumin. Low levels of this protein can be a sign of inflammation. Some of the drugs given for IBD, for example azathioprine, methotrexate, and some 5ASA drugs (such as mesalazine) can affect the liver. LFTs are a good way of checking for this.

Urea and Electrolytes (U&E)

U&E tests measure the levels of Urea, Creatinine, and Electrolytes (dissolved body salts such as potassium and sodium) in the blood. They are usually carried out to assess how well the kidneys are working. This test can also be used to check for dehydration (a common effect of acute diarrhoea). Regular U&E tests are often recommended for people on IBD drug treatments.

Ferritin and Transferrin Tests

Iron deficiency (a lack of iron) is one of the main causes of anaemia, a common complication of IBD. Symptoms of anaemia include fatigue, headaches and shortness of breath.

An FBC or full blood count (as described earlier) is one way of detecting iron deficiency. The doctors may also check your ferritin or transferrin saturation levels.

Ferritin is a protein in the blood that tends to increase with inflammation, so can be used as an inflammatory marker. It also stores iron and a low level of ferritin is usually a good indicator of low iron levels.

Transferrin, another blood protein, binds to iron to carry it from the gut. A transferrin saturation test shows how much of the transferrin in the body is actually carrying iron. A low transferrin saturation reading is another sign of iron deficiency.

Vitamin B12 and Folic Acid

Your blood may also be tested for Vitamin B12 and folic acid. These important vitamins work together to form healthy red blood cells.

Vitamin B12 is absorbed into the blood stream from the terminal ileum (the last part of the small intestine before it joins the colon). If the ileum is very inflamed or damaged, or has been removed by surgery, the body may not be able to absorb enough Vitamin B12, in which case it can be given by injection.

Low folic acid levels can be caused by poor nutrition or poor absorption from the small intestine. Some medications for IBD, such as methotrexate and sulphasalazine (a 5ASA drug), can also affect folic acid levels.

Other Blood Tests

Other blood tests that may be helpful in IBD include:

  • Tests for calcium and phosphate. Both these minerals are important for bone health. Vitamin D levels may also be measured if bone loss is suspected.
  • A magnesium check. Magnesium is needed for healthy muscles and bones. Severe diarrhoea may cause low magnesium levels, so a blood test may be needed to check this.
  • Tests for trace elements, such as zinc, selenium, chromium and other minerals which are usually found in tiny quantities in the blood of healthy people. These may be checked if you have Crohn’s disease affecting the small bowel or on long-term nutritional treatment.
  • A TPMT (thiopurine methyltransferase) test. This test can help predict who is more likely to experience side effects from thiopurine drugs such as azathioprine or mercaptopurine. However, it cannot identify everyone who may be affected.
  • Screening tests. Before you start on certain immunosuppressant or anti-TNF drugs, such as infliximab or adalimumab, you may need to be screened for infectious diseases such as Hepatitis B or C, tuberculosis, HIV, or chicken pox.
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