Gastrointestinal Tests PDF

Gastrointestinal Tests Dr Karan Rana Learning Outcomes Develop an understanding of malabsorptive disorders. Familiarise yourself with the variety of tests which can be used to differentiate between each condition. Coeliac disease  Malabsorption of nutrients.  Most common small bowel ent...

Gastrointestinal Tests Dr Karan Rana Learning Outcomes Develop an understanding of malabsorptive disorders. Familiarise yourself with the variety of tests which can be used to differentiate between each condition. Coeliac disease  Malabsorption of nutrients.  Most common small bowel enteropathy in Western world (1 in 200 in Europe).  Intolerance to ingested gluten (storage protein) found in wheat, rye and barley.  Symptoms such as diarrhoea, weight loss, retarded growth and secondary anaemia. Coeliac disease  Untreated patients have anti-tissue transglutaminase IgA antibodies which show high sensitivity (85%) and high specificity (97%).  Total IgA should be measured where Coeliac disease is suspected as 1 in 50 patients are IgA deficient.  If IgA deficient, measure IgG antibodies to tissue transglutaminase although this is less specific.  Confirm by biopsy.  Done with gluten challenge.  Short villi. normal coeliac Malabsorption  Anaemia.  Iron, folate and vitamin B12 deficiency.  Measure mean red cell volume, mean corpuscular haemoglobin, serum ferritin, vitamin B12 and folate.  Weight loss, oedema.  Reduced absorption of protein and nutrients.  Measure serum albumin, calcium and phosphate. Lactase deficiency Lactase deficiency  Lactase persistence is due to a single nucleotide change in a cis-acting enhancer upstream of the lactase gene.  Affected individuals have abdominal cramps and diarrhoea.  Tests:  Blood glucose response after 50g oral lactose is low < 1.1 mmol/l above baseline.  Breath hydrogen in response to lactose ingestion.  Assay biopsy for lactase activity. Fat malabsorption  14C-triolein test.  Fast patient overnight.  Collect basal sample of expired CO2.  Give 10 µCi of 14C-triolein in 60 g fat meal.  Collect 1 mmol sample of expired CO2 hourly for 6-7 h.  Measure radioactivity of CO2 samples.  Involvement of radioisotopes limits use!! Fat malabsorption specific activity of expired CO2 normal malabsorption 0 1 2 3 4 5 6 Time (h) Fat malabsorption  Positive test could be due to:  Cholestatic liver disease - no bile salts.  Pancreatic disease - no triglyceride lipase.  Intestinal origin (coeliac disease, Crohn’s disease, bacterial overgrowth with bacterial deconjugation of bile salts which are not absorbed and which in the colon cause diarrhoea).  Situation resolved by biopsy coupled with tests of hepatic and pancreatic function. Bile salt malabsorption  Normally actively absorbed in the ileum and travel back to the liver for reuse – enterohepatic circulation.  Detected by:  Whole body retention of selenium labelled homotaurocholic acid.  Retention after 30 min and 7 days is recorded by a gamma camera or whole body scanner.  < 10 % retention after seven days is considered abnormal.  Expensive and time consuming test. Bile salt malabsorption  Normally actively absorbed in the ileum and travel back to the liver for reuse – enterohepatic circulation.  Detected by:  Serum 7 a-hydroxycholestenone is an intermediate in the synthesis of bile acids from cholesterol.  If there is elevated bile acid synthesis, such as occurs in bile acid malabsorption, its concentration in serum increases.  Non invasive test performed by HPLC. Breath H2 tests  Used to detect bacterial overgrowth.  Drink lactose loaded drink (10 g).  Breath analysed for hydrogen.  Normally very little hydrogen produced.  Undigested lactose produces H2.  Takes 2-3 h.  NB: 50 g glucose may be used to detect bacterial overgrowth. Breath H2 tests Inflammatory Bowl Disease  Many possible causes e.g.  Malabsorption, laxatives, irritable bowel syndrome and inflammatory bowel disease.  Biochemical investigations must be conducted along with microbiological tests e.g. for C. difficile.  Laxative abuse is quite common - test urine sample for stimulant laxatives such as bisacodyl and senna.  Faecal osmotic gap (mosmol/kg) = 290 – 2 x ([faecal sodium] + [faecal potassium])  Summary Malabsorptive disorders consists of a variety of conditions, - Coeliac disease - Lactase deficiency - Fat malabsorption - Bile salt malabsorption Malabsorptive disorders present with very specific symptoms which can be used to identify which biochemical and non-biochemical tests are best to use.