Gastrin is a hormone produced by G cells in the stomach lining. Its primary job is to stimulate the production of hydrochloric acid, which your stomach needs to break down food and absorb certain nutrients. The system is designed to self-regulate: when acid levels rise high enough, gastrin production is suppressed. When acid is low, gastrin rises to compensate. This feedback loop means that gastrin levels can reveal important information about what is happening in the stomach.
The most common reason for elevated fasting gastrin in clinical practice is proton pump inhibitor (PPI) use. PPIs suppress acid production, which causes gastrin to climb as the body tries to restore normal acid levels. In people taking long-term PPIs, moderately elevated gastrin is an expected finding. Testing gastrin while on PPIs can still be useful, but interpreting the result requires knowing the medication context.
Beyond medication effects, significantly elevated gastrin may indicate conditions worth investigating further. Zollinger-Ellison syndrome, caused by a gastrin-secreting tumour (gastrinoma), produces very high gastrin levels alongside excessive acid secretion, recurrent ulcers, and diarrhoea. This is rare, but fasting gastrin is a key part of its investigation. Elevated gastrin can also be seen in atrophic gastritis, H. pylori infection, and chronic kidney disease.
Low gastrin is less commonly tested for, but can indicate reduced stomach acid production (hypochlorhydria), which affects nutrient absorption and may increase susceptibility to certain gut infections. Your practitioner will interpret your gastrin result alongside your medication history, symptoms, and any other relevant test results.
To investigate persistently elevated stomach acid, suspected gastrin-secreting tumours (gastrinomas), H. pylori-related gastric function changes, and to monitor gastrin levels in patients on long-term proton pump inhibitors.
