LABORATORY TESTS FOR GASTRIC ANALYSIS
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Hollander’s test (Insulin hypoglycemia test):
In the past, this test was used for confirmation of completeness of vagotomy (done for duodenal ulcer). Hypoglycemia is a potent stimulus for gastric acid secretion and is mediated by vagus nerve. This response is abolished by vagotomy.
In this test, after determining BAO, insulin is administered intravenously (0.15-0.2 units/kg) and acid output is estimated every 15 minutes for 2 hours (8 post-stimulation samples). Vagotomy is considered as complete if, after insulin-induced hypoglycemia (blood glucose < 45 mg/dl), no acid output is observed within 45 minutres.
The test gives reliable results only if blood glucose level falls below 50 mg/dl at some time following insulin injection. It is best carried out after 3-6 months of vagotomy.
Fractional test meal:
In the past, test meals (e.g. oat meal gruel, alcohol) were administered orally to stimulate gastric secretion and determine MAO or PAO. Currently, parenteral pentagastrin is the gastric stimulant of choice.
Tubeless gastric analysis:
This is an indirect and rapid method for determining output of free hydrochloric acid in gastric juice. In this test, a cationexchange resin tagged to a dye (azure A) is orally administered. In the stomach, the dye is displaced from the resin by the free hydrogen ions of the hydrochloric acid. The displaced azure A is absorbed in the small intestine, enters the bloodstream, and is excreted in urine. Urinary concentration of the dye is measured photometrically or by visual comparison with known color standards. The quantity of the dye excreted is proportional to the gastric acid output. However, if kidney or liver function is impaired, false results may be obtained. The test is no longer in use.
Spot check of gastric pH:
According to some investigators, spot determination of pH of fasting gastric juice (obtained by nasogastric intubation) can detect the presence of hypochlorhydria (if pH>5.0 in men or >7.0 in women).
Congo red test during esophagogastroduodenoscopy:
This test is done to determine the completeness of vagotomy. Congo red dye is sprayed into the stomach during esophagogastroduodenoscopy; if it turns red, it indicates presence of functional parietal cells in stomach with capacity of producing acid.
- Volume of gastric juice: 20-100 ml
- Appearance: Clear
- pH: 1.5 to 3.5
- Basal acid output: Up to 5 mEq/hour
- Peak acid output: 1 to 20 mEq/hour
- Ratio of basal acid output to peak acid output: <0.20 or < 20%