Gastrin is a hormone that stimulates the release of gastric acid to help break down food in the stomach. A healthcare provider may test gastrin levels if certain gastrointestinal symptoms persist, as high levels can be an underlying cause of these issues.
Gastrin’s Function and Control
Gastrin is a peptide hormone produced by G-cells in the lining of the stomach and upper small intestine. The arrival and distention of the stomach from food, particularly proteins, triggers G-cells to release gastrin into the bloodstream. Once circulating, gastrin travels to other cells within the stomach lining to initiate digestion.
The hormone’s primary role is to stimulate parietal cells in the stomach to secrete hydrochloric acid (HCl). This gastric acid creates the acidic environment needed to activate pepsin, an enzyme that breaks down proteins. Gastric acid also kills most microorganisms ingested with food, minimizing the risk of gut infections.
Beyond acid production, gastrin promotes the growth and maintenance of the stomach lining. It also increases the stomach’s muscular contractions, or motility, to help mix food and move it into the small intestine. Gastrin also stimulates the pancreas to secrete digestive enzymes and the gallbladder to release bile for food absorption.
Gastrin is managed by a negative feedback system. As the stomach produces acid and its pH level drops, G-cells are signaled to reduce gastrin secretion. When the stomach empties, another hormone called somatostatin is released, which inhibits the G-cells and turns off gastrin production until the next meal. This loop ensures gastric acid is produced only when needed.
Conditions Associated with High Gastrin
High blood gastrin levels, or hypergastrinemia, can result from several medical conditions that disrupt the feedback system controlling its production. The consequences depend on whether the high gastrin is accompanied by high or low stomach acid.
A rare cause of very high gastrin is Zollinger-Ellison syndrome (ZES), characterized by gastrin-producing tumors called gastrinomas. These tumors, found in the pancreas or duodenum, are not regulated by the body’s feedback mechanisms. They continuously secrete large amounts of gastrin, leading to high levels of gastric acid, which can cause severe peptic ulcers and chronic diarrhea.
A common cause of high gastrin is the long-term use of acid-suppressing medications like proton pump inhibitors (PPIs) and H2 blockers. These drugs reduce stomach acidity, causing the body to compensate by increasing gastrin production. Chronic infection with Helicobacter pylori can also damage the stomach lining, impairing acid secretion and triggering a rise in gastrin.
Another cause is atrophic gastritis, where the stomach lining is chronically inflamed and acid-producing cells are destroyed. This can result from an autoimmune response or long-term H. pylori infection. With fewer cells to produce acid, the stomach’s pH rises, leading to an elevation of gastrin as the body tries to stimulate the remaining cells.
Conditions Associated with Low Gastrin
Low gastrin levels, or hypogastrinemia, are less common and rarely a clinical concern. This condition can arise from damage to the gastrin-producing G-cells or from a lack of stimulus for its release. The primary consequence is reduced secretion of gastric acid, which can impair protein digestion and increase the risk of bacterial overgrowth. Low gastrin levels have also been associated with hypothyroidism.
Medical Testing for Gastrin
A gastrin test measures the hormone’s concentration in the blood. It is ordered for symptoms like recurrent peptic ulcers, severe abdominal pain, or chronic diarrhea that do not respond to standard treatments. The test helps determine if gastrin overproduction is the underlying cause.
Proper preparation is important for accuracy. Patients must fast for 12 hours before the blood draw, though water is permitted. Alcohol should be avoided for at least 24 hours before the test. Medications that reduce stomach acid, like PPIs, can affect gastrin levels and may need to be paused under a doctor’s guidance.
Results are interpreted alongside the patient’s symptoms and gastric acid levels. Normal fasting gastrin levels are less than 100 pg/mL. Moderately elevated levels may suggest atrophic gastritis or PPI use, while very high levels can point to Zollinger-Ellison syndrome. If results are inconclusive, a gastrin stimulation test may be performed to help differentiate the cause of the high levels.