What is being tested?
Gastrin is a hormone produced by “G-cells” in the part of the stomach called the antrum. It regulates the production of acid in the body of the stomach during the digestive process. This test measures the amount of gastrin in the blood to help evaluate an individual with recurrent peptic ulcers and/or other serious abdominal symptoms.
When food is eaten, the antrum of the stomach becomes distended and the presence of food stimulates the release of gastrin. Gastrin in turn stimulates parietal cells to produce gastric acid. Acidity helps to digest food and the rise in acidity eventually suppresses gastrin release. This feedback system normally results in low concentrations of gastrin in the blood, especially in the fasting state. Rare conditions such as G-cell hyperplasia and gastrinomas, including Zollinger-Ellison (ZE) syndrome, can cause an overproduction of gastrin and gastric acid. This can lead to aggressive peptic ulcers that can be difficult to treat.
Gastrinomas are gastrin-producing tumors. ZE syndrome is a condition caused by the presence of one or more gastrinomas and is characterized by high gastrin levels, greatly increased gastric acid production, and by peptic ulcers. Gastrinomas usually form in the pancreas, even though the endocrine cells of the pancreas do not normally make gastrin. More than half of them are malignant, causing cancer that can spread to other parts of the body, such as the liver. Even tiny tumors can produce large quantities of gastrin.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
You should fast for 12 hours and avoid alcohol for 24 hours prior to the test. Your health care practitioner may also ask you to refrain from taking certain stomach medications for several days prior to the test. Medications that can increase gastrin levels include antacids, H2-blocking agents (such as cimetidine), and proton pump inhibitors (such as omeprazole). These prevent the normal negative feedback in which acidity suppresses gastrin production.
How is it used?
The gastrin test is primarily used to help detect excess production of gastrin and gastric acid. It is used to help diagnose gastrin-producing tumors called gastrinomas, Zollinger-Ellison (ZE) syndrome, and hyperplasia of G-cells. G-cells are specialized cells in the stomach that produce gastrin, which in turn increases the production of gastric acid.
A gastrin test may also be used to monitor for recurrence following the surgical removal of a gastrinoma.
A gastrin stimulation test therefore may be used to provide additional information if the initial gastrin test result is moderately but not significantly elevated and the healthcare practitioner suspects that a person’s symptoms are due to a gastrinoma. This procedure involves collecting a baseline gastrin sample, giving the patient a chemical (typically the hormone secretin) to stimulate gastrin production, and then collecting additional blood samples at timed intervals for gastrin testing. The other (benign) causes of elevated gastrin will not show an increase after secretin administration.
A measurement of gastric acid pH level may sometimes be ordered along with or following a gastrin test to help diagnose ZE syndrome.
When is it ordered?
A gastrin test may be ordered when a person has diarrhea, abdominal pain, and/or recurrent peptic ulcers that do not respond to treatment and that the healthcare practitioner suspects are due to excess gastrin production. A gastrin stimulation test may be ordered when a gastrin level is moderately elevated and the healthcare practitioner suspects that a person has a gastrinoma.
When a gastrin-producing tumor has been removed, a gastrin test may be ordered periodically as a screening test to monitor for recurrence.
What does the test result mean?
Low or normal blood levels of gastrin are not typically of concern.
Moderately increased levels may be seen with a variety of conditions such as ZE syndrome, G-cell hyperplasia, chronic atrophic gastritis (a condition resulting from long-term inflammation of the stomach lining that leads to the loss of acid-producing cells), pernicious anemia, a pyloric obstruction (blockage at the junction of the stomach and duodenum), and chronic kidney failure.
Greatly increased levels of gastrin in symptomatic individuals and concentrations of gastrin that increase significantly during a gastrin stimulation test indicate the likelihood that a person has ZE syndrome and one or more gastrinomas. Imaging tests may be ordered as a follow up to high gastrin concentrations to locate the gastrinoma(s). The quantity of gastrin produced is not related to either the tumor size or to the number of tumors. Even tiny tumors can produce large amounts of gastrin.
Gastrin levels that were initially low after the surgical removal of a gastrinoma and then increase may signal a recurrence of the tumor. Concentrations that do not decrease after treatment may indicate that the treatment has not been fully effective.
Is there anything else I should know?
Gastrinomas can affect anyone, but people who have an inherited condition called MEN-1 (Multiple Endocrine Neoplasia, type 1) are at an increased risk. These people have genetic alterations that increase their lifetime risk of developing tumors in their pancreas or in another of their endocrine glands.
It is important to note that most stomach ulcers are not due to gastrinomas. They are commonly associated with Helicobacter pylori infections and sometimes with the use of nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen.
Gastrin levels commonly increase with age and with prolonged use of medications such as antacids and proton pump inhibitors that neutralize or inhibit the production of stomach acid. They will also typically be elevated in people who are not fasting. Increases in gastrin concentration with age may reflect a general decrease in the ability to produce stomach acid.
Gastrin blood levels follow a circadian rhythm. This means that they will be at their lowest between about 3 to 7 AM. Concentrations will be higher during the day and will fluctuate in response to meals.
What is Zollinger-Ellison syndrome?
Zollinger-Ellison (ZE) syndrome is a rare disease of the gastrointestinal tract. It is characterized by severe recurrent peptic ulcers in the stomach, duodenum and/or the upper portion of the small intestine. The ulcers are caused by a greatly increased amount of stomach acid due to high levels of gastrin, the hormone that stimulates stomach acid production. In ZE, high gastrin levels are caused by gastrin-producing tumors called gastrinomas, which usually form in the duodenum but can be found in the pancreas and rarely in other parts of the body. More than half of them are malignant and can metastasize to other parts of the body, such as the liver. The tumors must be removed surgically, and sometimes total removal of the stomach is necessary to control the acid production.
How long will it take to get the results of my gastrin test?
Gastrin testing is performed using specialized equipment in a laboratory and not every laboratory will offer gastrin testing. In some cases, your sample may need to be sent to a reference laboratory and results may take a few days.
Can’t I just take stomach medicines to address my excess gastrin and stomach acid?
Stomach medications such as proton pump inhibitors may be prescribed as part of your treatment, but it is important to diagnose your underlying condition. Although gastrinomas are rare, more than half of them are cancerous and can spread to other parts of your body.
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