TESTS FOR GASTRIC ACID SECRETION

Principle

The tests are based on the principle of measuring basal acid output (BAO) and maximal acid output (MAO)produced by the stomach under the influence of stimulants. These are then compared with the normal values.

Procedure

•• Patient is advised to fast overnight.

•• The stomach is intubated.

•• Measurement of acid secretion in 2–4 samples collected at an interval of 15 minutes, before stimulation is the basal acid output. It is expressed as mEq/hr.

•• The stomach is then stimulated by a stimulant to secrete maximal acid and 4 samples are collected again at interval of 15 minutes. This is maximal acid output and is expressed as mEq/hr. 

Stimulants Used for the Test

The different tests for gastric acid secretion are named depending upon the stimulant used for maximal acid output. Few commonly used stimulants are:

•• Histamine: It was the first stimulant used for the test and is injected subcutaneously.

•• Penta gastrin: It is the most commonly used and its action is similar to gastrin.

•• Insulin meal (Hollander test): The principle of the test is that in hypoglycemic state, the direct vagal action on parietal cells causes acid secretion.

•• Tubeless analysis: A resin-bound dye called diagnex blue is administered orally. The release of dye by the action of gastric acid and its appearance in the urine indicates the presence of gastric acid. The test can be repeated after giving any stimulants.

Significance: Basal acid output and maximal acid output.

Increased in:

•• Duodenal ulcer

•• Zollinger Ellison syndrome.

Decreased in:

•• Pernicious anemia—atrophic gastritis.

•• Achlorhydria (with ulcer in the stomach suggests a gastric malignancy).

OTHER TESTS

Tests for Pepsin 

Pepsin inhibitors are used for testing pepsin release from pepsinogen. Pepsin is decreased in atrophic gastritis.

Tests for Mucus

In this, the protein content of mucus is measured which is increased in hypertrophic gastritis.

Test for Intrinsic Factor

•• Intrinsic factor (IF) is required for absorption of vitamin B12 in the small intestine.

•• Intrinsic factor deficiency causes pernicious anemia. Schilling test is used for the diagnosis of pernicious anemia.

Test for Blood

Benzidine test or guaiac test detects blood. The test is positive in hematemesis/bleeding in the gastrointestinal tract or due to trauma of intubation.

Test for Gastrin

Serum gastrin is secreted by G cells present in the antropyloric region and proximal duodenal mucosa. It may be tested by the following tests:

Serum gastrin levels: Radioimmune assay (RIA) is commonly used for estimation of serum gastrin.

Gastrin provocation tests: These tests are used to differentiate between gastric acid hypersecretion and hypergastrinemia.

•• Secretin test: Secretin is intravenously injected.

•• Calcium infusion test: In this test calcium gluconate is given intravenously for 3 hours. In Zollinger Ellison syndrome, characteristically, serum gastrin levels rise by more than 50% of basal value in both the above mentioned tests. High levels are found in:

•• Atrophic gastritis

•• Zollinger Ellison syndrome.

Points to note:

•• Gastric analysis consists of tests for gastric acid, pepsin, mucus, intrinsic factor, blood and gastrin.

•• Gastric acid, both basal acid output and maximal acid output, are mainly increased in duodenal ulcer and Zollinger Ellison syndrome. It is decreased in pernicious anemia which also shows intrinsic factor deficiency.

•• High levels of gastrin are found in atrophic gastritis and Zollinger Ellison syndrome.