Gastrointestinal Module
Clinical Tests
Learning Objectives
By the end of this section, you will be able to:
- Describe the procedure or basis of common laboratory tests associated with GI function
Test for GI Functions
As you read through the following tests, consider what information or insights the test result could offer with regards to a patient’s GI health or disease.
D-xylose Absorption Test
Xylose is a monosaccharide not present in diet.
- Patient refrains from eating or drinking 8 – 12 hours prior
- Empties bladder before test
- Collect baseline sample (urine or serum)
- Drink 500 mL water containing 25 g of d-xylose
- Collect urine over 5 hours or draw blood sample at 2 hour to measure d-xylose
See HealthLink – D-Xylose Absorption Test for more details.
Endoscopy (upper GI or colonoscopy)
A small flexible tube with a camera and light is passed through the mouth down into upper GI to examine the lining of the stomach and duodenum (Upper GI Endoscopy) or through the anus up to the rectum and colon (Colonoscopy). If bleeding is discovered, an instrument passed through the tube can be used to cauterize the site. Similarly, a biopsy may be taken if required.
Erythrocyte Sedimentation Rate (ESR)
Whole blood samples is loaded into a thin tall tube and placed vertically. After 1 hour, the level (in mm) of plasma at the top of the tube is measured. The more red blood cells that fall to the bottom of the test tube in one hour, the higher the ESR.
When inflammation is present in the body, certain proteins cause red blood cells to stick together and fall more quickly than normal to the bottom of the tube.
See HealthLink – Sedimentation Rate for more details.
Fecal Calprotectin
Test measures concentration of calprotectin in stool. During GI inflammation, neutrophils get activated and release calprotectin in the intestines. It helps to differentiate between Irritable Bowel Syndrome (IBS) and Inflammatory Bowel Disease (IBD).
In BC, level > 40 μg/g is indicative of IBD.
Fecal Fat
- Patient consumes 100g/day of medium chain triglycerides for 48 hours before and during the collection period
- Fecal collection for 72 hours
- Measure the amount of fat; reported as g/24 hr
See HealthLink – Stool Analysis for more details.
H. Pylori Test
Test for most common cause of peptic ulcers. There are several different tests available, conducted on samples of: blood, breath, stool, or gastric biopsies.
See HealthLink – Helicobacter Pylori Test for more details.
Lactose Intolerance Test
- Patient fasts for 8 – 12 hours prior
- Collect baseline serum sample
- Ingest 50g lactose in water
- Collect serum samples at specified times, including 1 and 2 hours.
- Measure glucose in the serum
Alternative test: baseline & post 50g lactose ingestment measurement of H2 determined by breathing into a balloon-like container.
Pentagastrin Stimulation Test
Pentagastrin is, a 5 amino-acid long peptide, the active part of gastrin. This is an invasive procedure. Please note that pentagastrin stimulation test should not be confused with the calcitonin test.
- Patient fasts overnight
- Pass nasogastric tube into stomach
- Basal acid output (BAO) is determined by aspirating the gastric fluid for 1 hour
- Administer pentagastrin by intramuscular injection
- Aspirate gastric fluid for 1 hour to determine stimulated/maximal acid output (MAO)
- Measure pH, volume, determine the amount of H+ in each sample by titration
- Calculate BAO and MAO (mmol H+/hr)
Secretin Stimulation Test
Recall that secretin inhibits gastrin secretion by normal G cells.
- Patient fasts overnight
- Measures fasting serum gastrin for baseline
- Administer a bolus of secretin via IV
- Serum levels of gastrin are measured at 0, 2, 5, 10, and 15 minutes.
Note that gastrinoma cells actually increases gastrin release upon “stimulation” with secretin.
Serum Carotenoids
Carotenoids are naturally occuring pigments (e.g., carotene) found in vegetables and fruits. They are hydrophobic and insoluble in water. They must be absorved into the body in association with fat.
Tissue Transglutaminase Antibody Test
Draw blood from patient whose diet currently includes gluten. Individuals with Celiac disease often make auto-antibodies against tissue transglutaminase (Positive test in 98% of Celiac patients).
See HealthLink – Celiac Disease Antibody Test for more details.