IBS Fact : Evidence-based management of irritable bowel syndrome

Diagnostic testing for IBS: Part II


Virtual colonoscopy

Virtual colonoscopy, also known as computed tomography (CT) colonoscopy, is an imaging technique that uses X-rays to create images of the colon. These images are assembled by a computer to produce a three-dimensional representation of the colon on a computer screen (hence virtual), which is then examined by a gastroenterologist. The technique is less invasive than conventional colonoscopy since the X-rays are applied from an external source and no physical colonoscope is required – although a thin tube still needs to be inserted a short distance into the rectum to slightly inflate the colon for better visibility. Virtual colonoscopy is mainly used to detect tumors, polyps and diverticulitis, which it does with high accuracy. The main advantage of virtual colonoscopy is its non-invasive character. The procedure itself is not painful and requires therefore no sedation. Accordingly, patients can return to their normal daily activities immediately after the test, which takes only about 20 minutes. Despite these advantages, virtual colonoscopy has two major limitations. Firstly, since no physical colonoscope is used, any found polyps cannot be removed in the same session, and a second conventional colonoscopy session is required for this. Secondly, inflamed areas of the colon cannot be detected or sampled by virtual colonoscopy, i.e. no biopsy can be taken. Because of these limitations, the method is less suitable in the context of IBS where direct viewing of the colonic wall is necessary to differentiate between IBS and other inflammatory conditions such as IBD or colitis. Virtual colonoscopy is also not suitable for pregnant women, as the X-rays may cause an abnormality to the unborn child.

The Preparation for a virtual colonoscopy requires a bowel-cleansing regimen similar to that of conventional colonoscopy. This includes laxatives and a restrictive diet the day before the examination. The procedure itself is similar to a CAT scan. As a patient, you will be placed on a moveable examination table and slid into the doughnut-shaped CT scanner which takes the images. The nurse or physician will insert a thin tube a short distance into your rectum to slightly inflate the bowel for better visibility. This may be somewhat uncomfortable but is not painful. During the scanning, you will be asked to change position and hold your breath to obtain clear images from various angles. Pillows and straps may also be used to help you hold the correct position. The scanning is painless and takes about 20 minutes. After the scan, you will be able to resume all normal activities.

The obtained images will be reviewed by a radiologist and discussed with you immediately of forwarded to your general practitioner. Should any abnormalities be observed, a conventional colonoscopy may be required to further examine any suspicious areas, collect tissue samples or remove polyps.

In patients suffering from IBS only, virtual colonoscopy will not detect any abnormalities as IBS does not cause any visible alterations in the gastrointestinal tract. In such patients the persistence of abdominal complaints along with negative findings of the examination will be considered a confirmation of IBS.

In summary, virtual colonoscopy is a technique that uses x-rays to obtain images of the entire gastrointestinal tract. Its main advantage is the non-invasive and thus painless execution. The method is suitable to detect gastrointestinal tumors and polyps and may be considered for screening of individuals with an increased risk of such conditions. In the context of IBS, the method is less suitable as it cannot detect inflamed tissue and does not allow collection of tissue samples. Accordingly, virtual colonoscopy cannot be used to differentiate between IBS and several other conditions with similar symptoms. Here, classical colonoscopy remains the most reliable diagnostic method for patients with suspected IBS.

Upper gastrointestinal endoscopy (esophagogastroduodenoscopy)

As the name implies, this method uses a so-called endoscope which is a thin tube with a camera and a light source mounted on its top. The endoscope is inserted through the mouth to explore the upper gastrointestinal tract, i.e. the oesophagus, stomach and the first section of the small bowel. The technique is similar to colonoscopy with the exception that the endoscope is now inserted via the mouth and not the anus. 

The camera of the endoscope allows the physician to directly view the lining of the explored sections and to observe inflamed areas, ulcers, swellings or constrictions. Small tissue samples (biopsies) can also be collected for additional microscopic or laboratory examinations. In people with IBS-like symptoms, in particular diarrhoea, an upper GI endoscopy is mainly conducted to rule out or confirm coeliac disease. The examination consists of a sample biopsy from the small bowel and is carried out once the likelihood of coeliac disease has been confirmed by a blood test. Coeliac disease is confirmed if microscopic abnormalities are observed in the collected tissue samples. If no abnormalities are observed, the diagnosis of IBS is maintained and/or additional examinations are preformed to rule out other conditions. Statistically, coeliac disease turns out to be the underlying condition in 4% of patients with suspected IBS who suffer from diarrhoea or alternating diarrhoea and constipation. Preparation for the endoscopy involves refraining from eating or drinking for 6-8 hours prior to the appointment in order to ensure the upper gastrointestinal tract is empty. This is important to allow optimal visibility, but also to lower the risk of vomiting, which may be dangerous in sedated patients. Patients should also refrain from drinking alcohol on the day before the procedure. Detailed instructions are given to patients prior to the examination. Patients should inform their examining physician about any medications or supplements they are taking and any medical problems or special conditions they may have (e.g. pacemaker) well before the examination. Some medicines may need to be discontinued or adjusted before the procedure or afterward. Shortly before to the procedure, the patient is usually given drugs to relieve any pain, inhibit the gagging reflex, and to induce a mild sedation, which still allows the patient to cooperate during the procedure.

Because of the sedation, anyone who undergoes upper gastrointestinal endoscopy should be accompanied home by a friend or relative after the procedure. Once anesthetized, the patient is asked to swallow, while the endoscope is gently passed down the oesophagus into the stomach, and eventually into the first part of the small intestine. In patients with suspected coeliac disease, small tissue samples of the lining of the small intestine are then collected. These will be examined later under a microscope to determine whether tissue damage typical of coeliac disease can be observed. The procedure takes from 15 to 30 minutes, after which the patient is taken to the recovery area. Because of the sedation, there is no pain with the procedure, and patients seldom remember much about it. Following the procedure, some minor side effects such as bloating, nausea may persist for a short time and sore throat for up to two days. Serious side effects are very rare and may include chest pain, breathing difficulties, increasing swallowing or throat pain, vomiting, abdominal pain tar-coloured stool and fever. Medical care should be sought immediately should these symptoms occur. Overall, however, the procedure is very save and complications are unlikely. The results of the endoscopic examination are available right away, but your physician may want to share these with you at a later date when the sedation has subsided. A pathologist will examine the biopsy samples and will send a report to your physician to discuss them with you. If the endoscopic examination and collected tissue samples reveal an inflammation or tissue damage of the small bowel, coeliac disease may be diagnosed. This will require appropriate treatment consisting mainly of avoiding any dietary gluten. In contrast, since IBS does not cause any visible damage to the intestinal wall, an absence of inflammation along with persistent GI complaints may be considered a confirmation of true IBS.

Barium enema

A barium enema, also known as lower GI series, or double-contrast barium enema, or lower GI tract radiography, is a diagnostic procedure that uses a form of real-time x-ray called fluoroscopy and a contrast agent called barium to produce images of the lower GI tract. Air is sometimes used as a second contrast agent to expand the bowels for better visibility, hence double-contrast barium enema.


What does a barium enema visualize?

This method primarily visualizes the colon, and rectum, and sometimes the appendix and a portion of the small intestine. Abnormalities that can be detected include cancerous growths, diverticula (small pouches in the colon), fistula (an abnormal passage or channel between the anal canal and the skin around the anus), inflammation of the intestinal lining (Cohn’s disease or ulcerative colitis), polyps, ulcers, and obstruction. The procedure can often provide sufficient information to avoid the more invasive colonoscopy.


When is a barium enema prescribed?

Common symptoms or conditions that might require a barium enema include:


How should I prepare for the procedure?

For the exam to be successful, your lower digestive tract must be completely empty. You will therefore need to eat a diet consisting of liquids, low-fat and low-residue foods two or three days before the exam. The night before the exam, you will be asked to drink only clear liquids and to refrain from drinking or eating anything after midnight. You may also be prescribed a laxative and an over-the-counter enema to clear your lower tract the day before the exam.


How is de procedure performed?

The procedure is performed on an outpatient basis, usually in the morning. Upon arrival and an explanation of the procedure you will be changed into a gown and lie down on a special table that can be tilted to obtain images from various angles. A small, soft tube will be inserted into your anus and the barium contrast liquid will be infused into your colon. This is not painful, but will make you feel somewhat uncomfortable producing an urge to defecate. You will be asked not to expulse the liquid despite the urge. The tube in your anus will also prevent the contrast liquid from being released. Depending the type of examination, air may also be infused into your colon to obtain a better contrast (double contrast barium enema). The images of your colon will show up on a screen and will be interpreted and recorded by a specialist. You will be asked to hold very still and hold your breath for a couple of seconds at a time to obtain clear images in various positions. Once the examination is complete, the barium liquid will be released through the tube in your anus, and you will be allowed to go to a restroom to expel any remaining liquid. You may also be given a laxative and an enema to remove any residual the barium from your colon. The complete examination usually takes 30 to 60 minutes.


What happens after the examination?

After the examination, you will be able to resume your daily routine. You may however be constipated during a couple of days and your stool may give a whitish colour. You may also need to visit the toilet more frequently to expulse any remaining barium. The images of your colon will be forwarded to your general practitioner who will discuss them with you.


Potential side effects.

Side effects of barium enema are very rare. The examination itself is not dangerous since no instruments are inserted into your colon. The examination does expose you to a small amount of radiation, since it is basically an X-ray of your bowels. The barium contrast liquid itself is not absorbed into your bloodstream and will therefore cause no side effects. Only in very rare cases, an allergic reaction may occur. Constipation is a more frequent side effect, and you will be required to increase your intake of liquids to prevent it. Should the constipation persist more than 2 days, you should consult your GP.


Interpretation of findings in suspected IBS

The barium enema may reveal the cause of your symptoms, such as an obstruction or inflammation of the colon or small bowel. This will prompt additional examinations and/or a dedicated treatment. Since IBS itself does not cause any visible changes to the bowels, absence of any abnormalities on barium enema in persons with persistent symptoms may be considered a confirmation of true IBS.


Lactose intolerance test

Lactose intolerance is the inability to digest lactose, the natural sugar in milk and dairy products. When undigested lactose enters the large intestine, it becomes fermented by intestinal bacteria causing symptoms such as flatulence, abdominal cramping, and diarrhoea. Since these symptoms are similar to those of IBS, a lactose intolerance test is often used to distinguish between the two conditions. Interestingly, the intestinal fermentation of undigested lactose also produces small amounts of hydrogen, which can be detected in the breath. Hence, by consuming a specific amount of lactose and subsequently measuring hydrogen in the breath, lactose intolerance can be measured, which is the principle of the hydrogen breath text.

Preparation for the test consists of eliminating any digestive processes or substances that may interfere with the measurement. This involves an overnight fast and abstaining from any liquids eight hours prior to the test. Smoking and certain antibiotics or drugs may also need to be discontinued. The actual test consists of collecting breath samples by blowing into a bag or tube, which are then introduced in the device measuring the hydrogen. The protocol starts with a baseline sample to determine the fasting level of breath hydrogen. A lactose-containing liquid is then ingested, and the breath is sampled again at intervals of 15 minutes for up to 2 hours. Once measurements are complete, the data are analysed and results discussed, either immediately or at a later time. Daily activities can be resumed immediately after completing the test as no drugs are involved. If results indicate lactose intolerance, the next step will consist of avoiding diary and milk products. This should resolve intestinal symptoms within 24-72 hours. If symptoms persist despite a lactose-free diet, additional tests may be required to determine if another condition, such as IBS, may also be involved. In case of negative results, i.e. no lactose insufficiency, and no improvement of symptoms when abstaining from diary products, the diagnosis of IBS may be made in conjunction with additional examinations.

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