The initial workup of the majority of gastrointestinal conditions is by blood tests. These often indicate areas that need further investigation, such as inflammatory markers in inflammatory bowel disease, or may be diagnostic such as TTG levels in coeliac disease. Allergy testing may be helpful in suspected food allergy, and may be either, by blood tests, or skin prick tests.
Newer less invasive methods, such as stool calprotectin, are now available, but, at present, will only indicate the presence of inflammation, and are non discriminatory for specific conditions.
Specific tests of the gastrointestinal tract are directed in three major directions. Radiology or x-rays will show the anatomy and will demonstrate areas of narrowing or abnormal positioning. Endoscopy, coupled with biopsy, will detect areas of inflammation, and function tests such as pH-impedance will help to study how things are working.
The most common investigations are listed and described below:
A small volume of contrast such as barium is swallowed, and the movement of the dye is followed, by x-ray, through the oesophagus, stomach, and duodenum. This is particularly useful in the investigation of children who are vomiting, and helps to exclude narrowing of the oesophagus, and upper gastrointestinal tract. It will also demonstrate malrotation, if the contrast is followed through to the duodeno-jejunal junction.
This test is well tolerated by most babies and children. Occasionally in babies who have feeding problems, a tube may be passed if they are unable to take sufficient contrast.
Colonic Transit Markers
This is a useful test in severe constipation. A capsule containing plastic shapes is taken by mouth; this is released into the intestine. A plain abdominal x-ray is then taken at a specific time, usually 3-5 days, depending on the number of markers used. A review of the x-ray shows whether the passage has been slow, and if the major problem is at the site of the rectum. This is of particular use in constipation that has been difficult to treat with conventional laxatives.
Barium Meal And Follow Through
This investigation involves a contrast such as barium. In this situation the dye is followed through the whole of the small intestine, and followed by x-ray. A larger volume of contrast is involved than a barium meal and it can take several hours for the dye to pass through, and several series of films are taken. It can indicate areas of narrowing, and also give an idea of transit through the intestine. It involves a fairly large dose of radiation, and so in many centres this is being superseded by nuclear magnetic resonance imaging, particularly in inflammatory bowel disease.
Intestinal Nuclear Magnetic Resonance Imaging
An increasing number of centers now have the availability of NMR. The advantages over conventional x-rays are the quality of the images, which when coupled with both intravenous and oral contrast, can enhance areas of inflammation, and it does not involve radiation. It is also possible to examine other organs such as the liver and pancreas. In paediatrics the disadvantages are that the child is isolated in a tube, its noisy, and some small children can become distressed. During the procedure the patient is asked to hold their breath and keep still to avoid movement artifact on the image. The most common contrast is lactulose, which is sweet and is usually well taken. If looking for inflammation it does require an intravenous catheter.
In small children who are unable to keep still or are distressed, a general anaesthetic may be required. This obviously means that in this group careful consideration must be weighed between that and the benefit.
This test is simple and non invasive. Using a contact gel and ultrasound probe good views can be obtained of solid organs such as the kidney, liver, and pancreas. Unfortunately it does not give much information concerning the gut. The one exception is that of pyloric stenosis.
Coupled with a Doppler probe flow through vessels can be examined, which is helpful, particularly in liver disease.
PH Monitoring/pH- impedance
This is a dynamic test, used to assess the degree of acid reflux coming up from the stomach. The basis of the test is the placement of a fine tube through the nostril into the oesophagus. It has two pH sensors, which are positioned just above the lower oesophageal sphincter. An exact placement is essential to obtain accurate results, and so it is checked by a plain abdominal x-ray. The tube is connected to a small portable monitor, with event markers which can indicate significant symptoms during the test, and also the timing of meals. The tube is left in situ for 24h. This is important, as reflux is episodic during the day.
In small babies and children, who are mainly taking milk, reflux may be missed using this test. This is because the refluxing liquid is milk not acid. In order to overcome this a different type of system has been used. This is impedance. The catheter in this situation contains eight recording electrodes. 2 record pH but the remainder measure changes in electrical change between them, this varies depending on the fluid or air passing them. The practical procedure is the same as for pH study. The advantage of this catheter is that non-acid reflux can be identified, and also the height of the refluxing fluid in the oesophagus can be measured.
Upper GI Endoscopy (OGDS)
As in adult gastroenterology this is a very useful test. It enables a visual inspection of the lining of the oesophagus, stomach, and duodenum. This is coupled with a biopsy, which is a small scraping of the lining. This investigation is particularly helpful looking for inflammation, or specific changes in diseases such as coeliac disease.
The technique is to use fiber optic endoscopes. The scope is combined with a small video camera, is flexible, and can be manipulated to the exact position. This is not painful, but swallowing the tube may be uncomfortable. In children the examination is performed under a general anaesthetic. An empty stomach is important and so the child has to be fasted for at least three hours. Air is passed through the scope during the procedure too dilate the lumen, a very rare complication is a perforation. It has to be stressed however, that this is very rare, and if any weakness is seen in the lumen the procedure is terminated.
Most patients have no discomfort after the test, although they may have a dry throat.
Colonoscopy is the passage of a flexible scope through the large intestine from the anus. A complete study includes the entire colon to the terminal ileum (the join of the small intestine and the colon). This investigation has become the mainstay for the investigation of inflammatory bowel disease.
In order that the lumen is well visualised the bowel has to be cleared. Therefore the patient is given laxatives the day before the procedure. Most children find this the most unpleasant part of the test!! Again young children are tested under a general anaesthetic. As in the case of OGDs perforation is a risk, but again it is very rare.
Following the test, most people experience no discomfort.