Gastrointestinal Tests PDF

Gastrointestinal Tests Dr Karan Rana Learning Outcomes  Knowledge and understanding of biochemical tests that can be used to investigate:  Gastric function.  Exocrine pancreatic function.  Conditions associated with malabsorption of nutrients.  Inflammatory bowel diseases....

Gastrointestinal Tests Dr Karan Rana Learning Outcomes  Knowledge and understanding of biochemical tests that can be used to investigate:  Gastric function.  Exocrine pancreatic function.  Conditions associated with malabsorption of nutrients.  Inflammatory bowel diseases. 2 Overarching theme  Biochemical function tests often need to be used together with other investigative procedures:  biopsy/histology, endoscopy, CAT scans etc.  Particularly true of most of the G.I. tract where access is relatively easy. 3 Endoscopes 4 Stomach  Peptic ulcer disease caused by Helicobacter pylori.  Invasive procedures:  Biopsy followed by:  Histology (98% sensitivity).  Urease (CLO) test on biopsy (90-95% sensitivity).  Colour change due to alkaline ammonia.  Non-invasive procedures:  Serology (IgG against H. pylori) – good sensitivity but poor specificity (false positives).  ELISA for stool antigens.  Breath test using [14C] or [13C] urea – eradication check.  Antibodies persist. 5 Urea breath test for H. pylori 6 Fasting plasma gastrin  Gastrin is released from the G cells in the gastric antrum in response to food intake and stimulates acid secretion.  Measured by immunoassay.  The most common reason for measuring fasting plasma gastrin is a gastrin secreting tumour (gastrinoma).  Patients with gastrinoma will have a high basal fasting acid secretion and as a consequence peptic ulcer disease. 7 Acute pancreatitis  Severe abdominal pain with acute inflammation of pancreas.  Caused by excessive alcohol, gall stones but many cases idiopathic (no cause identifiable).  Serum amylase > 10 times upper limit of normal is very strong evidence.  Amylase is a pancreatic enzyme which has leaked into the blood stream.  Lower elevations may be due to other causes:  perforated duodenal ulcer, intestinal obstruction, renal failure (amylase is quite small and is excreted in urine). 8 Chronic pancreatitis  Loss of pancreatic function, often due to chronic alcohol intake. Also autoimmune forms and in cystic fibrosis.  Serum amylase is normal or low.  Serum IgG4 level (>135 mg/dl) has a fairly high sensitivity to diagnose type 1 autoimmune pancreatitis.  Two types of biochemical test:  Non-invasive.  Invasive (not used any more). 9 Chronic pancreatitis – non-invasive  Pancreatic elastase 1 in stool (not degraded).  Non-invasive marker - low levels in faeces indicate exocrine pancreatic insufficiency.  Specificity and sensitivity of >90%  Determined by ELISA. Above 200 µg /g stool is considered normal  Note the test is not influenced by patients on the enzyme substitution therapy pancreatin. 10 Chronic pancreatitis – invasive  Secretin/CCK (cholecystokinin) test.  Patient fasts and double lumen radio-opaque tube positioned to aspirate gastric and pancreatic secretions.  Basal collection 2 x 10 min.  Intravenous secretin: 6 x 10 min collections. Healthy subjects show fluid secretion rate of 2.0 ml/kg body weight and bicarbonate concentration normally > 75 mM  Intravenous cholecystokinin: 2 x 10 min collections. Trypsin and amylase activities compared to local standards.  Research use only and as a ‘Gold standard’ to evaluate new tests 11 Chronic pancreatitis – invasive  Non-biochemical complement these.  Endoscopic ultrasonography provides excellent imaging and has the option of fine needle aspiration for cytology. 12  Summary The GI tract includes a vast array of organs which carry out distinct functions. Due to this variability there exists a variety of biomarkers, both biochemical and non-biochemical which can be used to investigate disorders of the GI tract. Acute and Chronic Pancreatitis, have distinct biomarkers/tests which better allows clinicians to distinguish the two.