[14C)GLYCOCHOLIC ACID BREATH TEST
This is performed to look for bacterial overgrowth. The patient is given 14C-labelled bile salts by mouth. Bacteria deconjugate the bile salts, releasing [14C)glycine, which is metabolized and appears in the breath as l4C02. This radioactivity in the breath can easily be measured. An early rise indicates either bacterial overgrowth in the upper small intestine or rapid transit to the colon where, of course, bacteria are normally present.
HYDROGEN BREATH TEST. This is frequently used as a screening test to detect bacterial overgrowth. Oral lactulose or glucose is metabolized by bacteria with the production of hydrogen. An early rise in the breath hydrogen will indicate bacterial breakdown in the small intestine. Rapid transit of the lactulose to the large intestine will also produce a rise in breath hydrogen. As bacteria are present in the oral cavity, the mouth should be rinsed out with an antiseptic mouthwash prior to the test being performed. This test is simple to perform and it does not involve radioisotopes. However, interpretation is often difficult.
DIRECT INTUBATION. Aspiration of intestinal juices is another method by which bacterial contamination can be detected. Bacterial counts are performed on aerobic and anaerobic cultures. Chromatography of bile salts can also be performed on the aspirate to detect evidence of deconjugation by bacteria.
PANCREATIC TESTS diagnosis of steatorrhoea.
OTHER BLOOD TESTS. Serum immunoglobulins are measured to exclude immune deficiencies. Hormones, e.g. VIP, are measured in high-volume secretory diarrhoea.
TEST FOR PROTEIN-LOSING ENTEROPATHY. Intravenous radioactive chromium chloride (SICrCI3) is used to label circulating albumin. In excess gastrointestinal protein loss, the faeces will contain radioactivity. This test is rarely required unless a low serum albumin is a major clinical feature.
BILE SALT LOSS. This can be demonstrated by giving oral 23-selena H,25-homotaurocholate (Se HeAT, a synthetic taurine conjugate) and measuring the retention of the bile acid by whole body counting at 7 days.
INTESTINAL PERMEABILITY TESTS. These tests can be used for the detection of small bowel disease but are not in general use. They are based on the fact that the abnormal intestinal mucosa is permeable to large molecules such as lactulose and cellobiose. An oral load of these sugars is given and the sugars are then measured in the urine. A radiolabelled sodium-EDT A solution has been used in a similar way and is said to be a more accurate investigation.
In many small bowel diseases, malabsorption of specific substances occurs, but these deficiencies do not dominate the clinical picture. An example is Crohn’s disease, in which malabsorption of vitamin Bl2 can be demonstrated, but this is not usually a problem and diarrhoea and general ill-health are the major features.
Steatorrhoea – malabsorption of fat – is discussed The major disorders of the small intestine that cause malabsorption are shown.