Tests and investigations

There are several blood tests that are used to help support a diagnosis of Crohn's or Colitis and to monitor the effects of Crohn's or Colitis and its treatments.

Blood samples are usually taken from a vein in the arm, using a needle attached to a syringe or a small collecting container. For some specialised tests you may be asked to fast (not eat) overnight or for a few hours before the sample is taken. Your doctor or nurse will let you know if this is necessary. You are likely to need repeat blood tests over time. Some of the blood tests used most often in Crohn's and Colitis are:

Full Blood Count (FBC)

Measuring the level of calprotectin (a protein contained in white blood cells) in a stool sample can detect active inflammation in the intestine.

The National Institute for Health and Care Excellence (NICE) recommends that faecal calprotectin tests should be used to distinguish IBD from other, non-inflammatory, conditions, such as Irritable Bowel Syndrome (IBS). The test can also be used to monitor whether you are responding to treatment.

The NHS has a bowel cancer screening programme for people aged 60 to 74 that uses a Faecal Occult Blood (FOB) test to check for hidden (occult) blood in the stool. See our information on Bowel cancer risk for further details.

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, thin, 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 (bottom) to look at the colon and rectum. The video camera relays images to a screen outside the body, allowing the endoscopist to have a clear view of the part of the gut they are examining.

• Biopsy. The endoscopist may also take biopsies (small samples of tissue) through the endoscope. This involves a small scraping of cells from the lining of the gut, which can then be examined under a microscope to give more information.
• Polyps. During endoscopy, it is possible to remove polyps (small mushroom- like growths on the inner lining of the colon that may, rarely over time, become cancerous). The endoscope can be fitted with a wire containing an electric current that can be used to remove the polyps. For more information on this procedure, see our leaflet: Bowel Cancer and IBD.
• Strictures. Endoscopists also use balloons (which are passed via the endoscope and inflated inside the gut) to dilate strictures (narrowings) of the gut.

Preparing for an endoscopy

The endoscopy staff will provide you with detailed instructions on how to prepare for your endoscopy, and will answer any questions you may have about the test. If you have sedation or a general anaesthetic you will need to arrange for someone to take you home and stay with you for the next six hours. Sedation affects your reflexes and judgment, so you will not be allowed to drive, take alcohol, operate heavy machinery or make any legal decisions for 24 hours.

Types of endoscopy

The main types of endoscopy are as follows:

Upper Gastrointestinal (GI) Endoscopy (or Gastroscopy)
This type of endoscopy is used to examine the upper part of the digestive system – the oesophagus (gullet), stomach, and duodenum (first part of the small intestine). It tends to be used more for Crohn’s than Colitis, but may be helpful to rule out Crohn’s when diagnosing Colitis.

The endoscope used for this type of examination is usually known as a gastroscope. It will be gently inserted through the mouth and down the oesophagus into the stomach and the first part of the small intestine. The windpipe can be easily avoided and your breathing will be unaffected. The stomach must be empty in order to get a clear view, so you will be asked not to eat anything for at least six hours before the procedure.

You will be offered the choice of sedation (administered into vein in your hand or arm) or a local anaesthetic throat spray (which works much like a dental injection).

Sedation makes you drowsy and relaxed, but not unconscious.  Although you will be able to follow simple instructions during the investigation it is unlikely that you will remember much afterwards about the procedure. If you have the throat spray you must not have anything to eat or drink until the sensation in your mouth and throat has returned to normal. Children will normally be offered general anaesthesia.

Colonoscopy

A colonoscopy is an examination of the colon (large intestine). Colonoscopies are often used to diagnose and to assess the extent and severity of Colitis and Crohn’s.

The endoscope used in a colonoscopy is known as a colonoscope. It is a narrow, 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 your anus, into your rectum and then on into your 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 Colitis or Crohn’s Colitis. Guidelines advise that most people should have a colonoscopy eight to 10 years after the start of Colitis or Crohn’s Colitis. Depending on what is seen, it is likely that follow-on colonoscopies will be recommended every one, three or five years. People who also have Primary Sclerosing Cholangitis are at an increased risk of colorectal cancer, and therefore surveillance colonoscopy is recommended at diagnosis, then every one to two years. Chromoendoscopy, which involves spraying special dyes onto the lining of the colon, is used to help to identify abnormal cells.

For colonoscopy to be successful, the colon has to be completely clean (empty of stool/faeces). To ensure that the colon is clear, you will be asked to take a laxative preparation around 24 hours before the procedure. It is important to follow the written instructions you will be given about taking the preparation, otherwise your test may be unsuccessful and will need to be repeated.

Similar to a endoscopy, you may be offered sedation for the colonoscopy to help you feel sleepy and relaxed. An alternative during colonoscopy, is nitrous oxide, known as ‘gas and air’. The advantage of nitrous oxide, which is commonly used to relieve pain in childbirth, is that the drug is quickly expelled from the body, allowing you to drive within 30 minutes of the procedure. Children are usually given a general anaesthetic.

If you are going to have a colonoscopy, some useful tips include:

• Make sure medical staff and the endoscopy team know about all the medications you are taking (including over the counter remedies, vitamin pills and supplements) in good time before your procedure. They also need to know if you have kidney disease, heart failure or allergies (including latex).
   
• You may be asked to discontinue oral anticoagulants (such as warfarin) for a few days before the endoscopy procedure due to risks of bleeding.
   
• Seven days before your endoscopy appointment, stop taking iron tablets as iron makes everything inside your bowel appear black and the lining hard to see.
   
• Four days before your endoscopy appointment, stop taking any medications that might cause you to become constipated (e.g. lomotil, loperamide or codeine phosphate).
   
• A few days before your endoscopy, you may be asked to avoid red meat and foods containing fibre (such as fruit, pulses or lentils, vegetables, and nuts/ seeds) since these remain longer in your digestive system than other foods.
   
• All foods and milk should be finished at the time written on your appointment letter.
   
• For the 24 hours before your appointment, you must only drink clear liquids. A liquid is considered ‘clear’ if you can read newsprint through it, i.e. apple juice is considered clear, while orange juice is not.
• The more liquid you consume the easier the bowel prep will be. You should drink at least a glass of water (about 250ml) or another clear fluid every hour while the effects of the medication persist. Fluids not only prevent dehydration, but play an important part in the bowel cleaning process.
   
• Some people find the taste of laxative preparations unpleasant. Suggestions for making the experience more agreeable include drinking through a straw placed far back on your tongue, chilling the preparation in the fridge, or mixing it with a cordial drink. It is a good idea to have water to hand to drink straight after consuming each glass of prep.
   
• Once you have started taking laxatives, it is advisable to stay near a toilet as you will experience frequent bowel movements. You can use a barrier cream, such as zinc and castor oil, on your bottom or a nappy rash ointment, to prevent soreness during your frequent trips to the toilet. Some abdominal cramping is normal.
   
• During many endoscopy tests, air is pumped into the colon to improve views of the bowel wall. If any air remains, you may experience sensations of bloating and cramping after the procedure. To help relieve this discomfort, try walking around, drinking warm drinks or peppermint water and taking a pain killer. It is probably better to avoid ibuprofen, diclofenac, and aspirin since these are non-steroidal anti-inflammatory drugs (NSAIDs) and studies suggest they may trigger a flare-up of Crohn's or Colitis. Paracetamol may be a safer option. If you have concerns, talk to your doctor or IBD team.

Sigmoidoscopy (or Proctosigmoidoscopy)
A sigmoidoscopy is similar to colonoscopy but only examines the rectum and sigmoid colon (the lower part of the colon). Usually a flexible endoscope is used, which allows the endoscopist to see further up the colon than if the non-flexible version is used. You may feel some discomfort, but this should pass once the examination is finished. Sigmoidoscopy is most useful for Crohn's or Colitis limited to the left side of the colon.

To give the doctor a clear view, it will be necessary for the lower part of the colon to be empty of faeces. To do this, you will need to have an enema (a liquid preparation which is squirted into the back passage to induce a bowel movement). An enema can be self-administered at home or by nursing staff when you arrive at the hospital. You may eat and drink normally until you have the enema, after which you can only have clear fluids until after the test.

The procedure, which usually takes around 10-20 minutes, is usually done without sedation, although you may be offered nitrous oxide. During sigmoidoscopy, biopsies may be taken and small polyps removed. Sigmoidoscopy is most useful for Crohn's or Colitis limited to the left side of the colon.

People with Colitis who have undergone an ileal pouch anal anastomosis (IPAA) procedure (where an artificial rectum has been created from the small intestine) may need to have the pouch examined with a sigmoidoscope to look for pouchitis (inflammation) and for routine cancer surveillance.

Single or Double Balloon Enteroscopy
This form of examination uses a special type of endoscope with one or two small balloons at its tip. By alternately inflating and deflating the balloons, (also known as push and pull endoscopy) the endoscope can be moved further into the small intestine than other types of endoscopes. It may be inserted through the mouth, or, less commonly, through the anus. It can be used to take biopsies, remove polyps and for dilatation (widening) of strictures. Since the procedure takes longer than other endoscopies, a general anaesthetic or sedative is generally advised.

Capsule Endoscopy
For this investigation, you will be asked to swallow a small capsule the size of a large vitamin pill. This is generally done after an overnight fast. The video 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. You will be allowed to go home wearing the data recorder, but should avoid strenuous exercise and bending over. The capsule is disposable and should pass out of the body naturally in a bowel movement. Biopsies cannot be taken with the capsule, and the capsule is not suitable for people with strictures or bowel obstructions as it can become stuck. Capsule endoscopy is normally only used when IBD is suspected but colonoscopy findings have been negative.

The patency capsule, which is about the same size as the video capsule, is sometimes used to identify whether patients are free of strictures and bowel obstructions and can safely undergo capsule endoscopy. Instead of the camera, the patency capsule contains a radioactive tag allowing it to be detected by an external radioscanner. The capsule, which is made from cellophane, starts to disintegrate if the passage of the device becomes blocked.

The x-ray and other similar imaging methods used in Crohn's or Colitis can have different benefits and risks in terms of, for example, exposure to radiation, image quality, or the need for anaesthetic.

Abdominal X-rays

Ordinary or plain abdominal X-rays do not show as much detail of the digestive system as some of the other imaging techniques (see below). However, they may be used in an emergency to diagnose bowel obstruction, perforation or megacolon (widening of the colon which may cause perforation).

Barium studies

Barium is a harmless white substance which is not absorbed into the body, but instead forms a temporary coating on the inside of the intestines. Since X-rays can not pass through barium, it is used to provide a clearer outline of the gut on X-ray pictures. Barium is introduced in different ways depending on the part of the gut needing imaging. For the upper part of the digestive system, you will be asked to swallow barium (known as a barium meal). For the small intestine (known as a barium follow through test), you will take barium by mouth and be asked to take a laxative the day before the test. You will also need to fast overnight.

To visualise the colon, a barium enema is used, delivering barium directly into the colon through a short tube placed in the anus. After taking barium, your faeces will turn pale and chalky looking for a few days and may be difficult to flush away. Barium studies have recently become less common for Crohn's or Colitis due to widespread availability of CT and MRI imaging (see below). CT and MRI offer the advantage of greater detail and information beyond the inner lining of the bowel (such as fistula or abscesses).

Chest X-rays

Biologics increase the risk of infections, such as tuberculosis (TB). Before starting biologics you will need to have a chest X-ray to rule out silent TB infection, which might be made worse by treatment. Whilst on biologics, people with Crohn's or Colitis who have travelled for more than a month to countries with high levels of TB should also consider having a chest X-ray.

DEXA (Duel 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 taking around 20 minutes. DEXA can show if bones have become thinner and weaker than normal – a condition known as osteoporosis. People with IBD have an increased risk of developing osteoporosis, particularly if they have been on steroids, or have low calcium levels. Annual DEXA scans are recommended for people taking steroids long- term. For more details, see our information on Bones.

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

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 put together to produce two-dimensional (2-D), or sometimes, three-dimensional (3-D) views of the body.
 
CT enterography (CTE) is an imaging test combining CT scanning with contrast material to improve the detail of the small intestine. Before the test, in some hospitals, you will need to drink a few glasses of liquid containing the contrast material. In other hospitals, you may only be asked to drink water. Then during the scan, a different type of contrast material will be injected into a vein in your arm. CTE improves the accuracy of diagnosis and allows good imaging of the entire thickness of the bowel wall. Occasionally, enteroclysis is used where a small tube delivers contrast material to where it is needed in the intestine, instead of the fluid being swallowed.

Advantages of CT and CTE include:

• Rapid scan times (about 10 minutes)
• The ability to examine the entire length of the small bowel
• Imaging children without sedation
• Quiet machines
• Widespread availability.
  
  

Also, unlike MRI scanners, the CT scanner does not surround your whole body so you should not feel claustrophobic (fear of enclosed spaces).

Disadvantages include exposure to ionizing radiation. It is considered good practice to minimise radiation where possible for people with IBD because they are likely to require many imaging studies, which could lead to a high total dose of radiation to the body.

Magnetic Resonance Imaging (MRI)

MRI scans use strong magnetic fields and radio waves to create images of the inside of the body. MRI scans do not use X-ray radiation. 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. MR enterography (MRE) is a special type of MR imaging that is performed with the addition of contrast material to produce better images. You will need to drink contrast material before the scan, and then during the scan a different type of contrast material will be injected into a vein in your arm. MRE improves the accuracy of diagnosis and allows good imaging of the entire thickness of the bowel wall.

The MRI scan can be noisy (due to the electric current in the scanner coils being turned on and off) so you may be provided with ear plugs or headphones to wear.

The scan can take from 15 minutes to over an hour and a half. This means that some people may find it uncomfortable, especially if they suffer from claustrophobia. However, for Crohn's or Colitis 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. If you feel anxious, you may want to ask for a mild sedative prior to your examination. It is important to lie very still during the scan to stop images becoming blurred, and you will need to follow instructions to hold your breath from time to time.

Advantages of MR and MRE include scans being free of radiation and the ability to explore the entire length of the small bowel. MRI scanners use magnets, which means that they are not suitable for people with electronic devices (such as pacemakers) or who have metal implants (such as artificial joints).

Some people may have an Magnetic Resonance Cholangiopancreatography (MRCP), which provides detailed images of the liver, gall bladder, bile ducts, pancreas and pancreatic ducts. The technique can be used to diagnose Primary Sclerosing Cholangitis.
 

Ultrasound

Ultrasound is another form of scan helpful in Crohn's or Colitis. Ultrasound scanners work by using 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. The scanner then picks up the echoes and converts them into an image. Ultrasound can show up thickening of the bowel wall, fistulas (abnormal channels linking different parts of the bowel), abscesses and strictures.

Advantages of ultrasound include no exposure to radiation, wide availability and being a comfortable procedure for patients. Before the scan, you will need to drink large amounts of liquid and to avoid eating for a few hours. Drinking a contrast agent before the scan can help improve the detection of inflammation.

Endoscopic Ultrasound Scans (EUS), involve using a special type of endoscope with a tiny ultrasound transmitter in the tip. As with a normal endoscope, EUS is inserted through the mouth to examine the upper part of the digestive system or through the anus to examine the colon and ileum. If necessary, your doctor will be able to take samples of cells. For the procedure you will usually be given a sedative or a local anaesthetic spray to numb your throat.

SeHCAT Scan

A SeHCAT scan is used to find out whether diarrhoea is caused by bile acid malabsorption (BAM). When you eat, bile salts (made in the liver and stored in the gall bladder) are released into the small bowel to help digest food. Normally, when bile salts reach the end of the small bowel, they are taken up by the blood. However, if the lower end of the small bowel is inflamed (due to Crohn’s Disease) or has been removed during surgery, bile salts may not be absorbed. Instead, bile salts enter the large bowel (colon) where they draw fluid from the blood, leading to diarrhoea.

The SeHCAT scan involves two separate appointments. At your first appointment, you will be asked to swallow a small capsule containing synthetic bile salts linked to a radioactive tracer. A little later, a scan will be taken using a special camera that identifies radioactivity. At the second appointment, a further scan will be done to measure the amount of synthetic bile salt remaining in your body, showing whether you have problems absorbing bile salts.

Apart from stopping certain drugs that interfere with the test results (Creon, colestyramine and colesevelam), you can eat, drink and take other medications as normal. No sedation is necessary.

There is no need to be concerned about the level of radiation since the radiation dose is low (equivalent to the amount received from natural sources of radiation in about two months), so you will not need to stay away from anyone. However, you may find some airports have sensitive radiation detectors that are triggered by the small amounts of radioactivity, which remain in your body for up to three months after the scan. Therefore, it is recommended you carry your appointment letter to show airport security officers.

If you have perianal Crohn’s, you may be given an anaesthetic so that the area can be examined while you sleep, since the examination is painful and it is helpful to have the anal sphincters and pelvic floor muscles fully relaxed. EUA is often used to investigate fistulas (abnormal channels, tunnels or passageways connecting one internal organ to another, or to the outside surface of the body), and sometimes a special probe is used to trace out the route of the fistula.
 
Studies show that pelvic magnetic resonance imaging (MRI) is more accurate than EUA at finding the course of perianal fistulas. However, EUA offers the advantage of also allowing any abscesses to be drained and other treatments to be given. For more details, see our information sheet: Living with a Fistula.

Endoscopy shows the macroscopic (visible to the human eye) appearance of the lining of the gut. Crohn’s can be identified by the presence of isolated areas of inflammation and Colitis by continuous areas of inflammation, with no gaps in between. The biopsies (tiny samples of tissue) that are taken during endoscopy will be examined under the microscope for features that are distinctive of Crohn’s or Colitis.

Generally, scans and X-rays show the location and extent of inflammation. This helps doctors to distinguish between Crohn’s (which can affect any part of the digestive system from mouth to anus) and Colitis (which affects only the large intestine). Cross-sectional imaging (such as CT and MRI) can show whether ulcers have spread through all layers of the bowel wall (as occurs in Crohn’s) or affect just the inner layers (Colitis).

• Living With Crohn's or Colitis
• Fatigue
• Taking Medicines
• Managing Bowel Incontinence
• Living With a Stoma

Health professionals can order some publications in bulk by using our online ordering system. If you would like a printed copy of a booklet or information sheet, please contact our helpline.

Our helpline is a confidential service providing information and support to anyone affected by Crohn's or Colitis. Our team can:
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