The stomach acid test is a test that assesses the quantity and acidity of stomach contents.

After a period of fasting, gastric residue is all that remains in the stomach. This fluid can be removed via a tube inserted through the esophagus.

To test the capacity of the parietal cells in the stomach to secrete acid, gastrin may be injected subcutaneously (just under the skin), intramuscularly, or intravenously. The stomach contents are then removed and analyzed.

Another test involves insulin-induced hypoglycemia. Enough insulin is given subcutaneously or intravenously to cause the blood sugar to decrease, which causes the vagus nerve to stimulate the release of gastrin. After a short time, the stomach contents are removed and analyzed.

You will be asked to consume no food or liquid for four to six hours before the test.

You may notice some discomfort and/or a gagging sensation as the tube is passed through your nose or mouth and down your esophagus.

This test may be used for a number of reasons:

• To test for the cause of ulcers
• To detect duodenal regurgitation
• To evaluate the cause of malabsorption
• To assess the adequacy of anti-ulcer medications
• To evaluate secretion of gastrin

Normally the volume of the stomach residue is 20 to 100 mL and the pH is acidic (1.5 to 3.5).

• Ulcers may be caused by delayed emptying or increased secretion of acid.
• The presence of bile in the stomach indicates regurgitation from the duodenum. This may occur after a partial gastrectomy. (See also gastroesophageal reflux disease.)
• Decreased levels of stomach acid or gastrin can cause malabsorption (inadequate absorption of nutrients from the intestinal tract).
• Increased levels of gastrin may cause increased secretion of acid and may lead to ulcers (Zollinger-Ellison syndrome).

There is a slight risk of the tube being placed through the trachea and into the lungs instead of through the esophagus and into the stomach. The health care provider will be sure the tube is correctly placed before continuing with the test.

If the test includes injection of insulin, there is a risk of inducing symptoms of hypoglycemia (low blood sugar).