Your doctor will base a diagnosis on the following:
- Medical history. Your doctor will ask about your signs and symptoms and review your medical history.
Blood tests. A sample of your blood is analyzed to see whether you have elevated gastrin levels. While elevated gastrin may indicate tumors in your pancreas or duodenum, it also can be caused by other conditions. For example, gastrin may also be elevated if your stomach isn't making acid, or you're taking acid-reducing medications, such as proton pump inhibitors.
You need to fast before this test and may need to stop taking any acid-reducing medications to get the most accurate measure of your gastrin levels. Because gastrin levels can fluctuate, this test may be repeated a few times.
Your doctor may also perform a secretin stimulation test. For this test, your doctor first measures your gastrin levels, gives you an injection of the hormone secretin and measures gastrin levels again. If you have Zollinger-Ellison, your gastrin levels will increase even more.
- Upper gastrointestinal endoscopy. After you're sedated, your doctor inserts a thin, flexible instrument with a light and video camera (endoscope) down your throat and into your stomach and duodenum to look for ulcers. Through the endoscope, your doctor may remove a tissue sample (biopsy) from your duodenum to help detect the presence of gastrin-producing tumors. Your doctor will ask you not to eat anything after midnight the night before the test.
Endoscopic ultrasound. In this procedure, your doctor examines your stomach, duodenum and pancreas with an endoscope fitted with an ultrasound probe. The probe allows for closer inspection, making it easier to spot tumors.
It's also possible to remove a tissue sample through the endoscope. You'll need to fast after midnight the night before this test, and you'll be sedated during the test.
- Imaging tests. Your doctor may use imaging techniques such as a nuclear scan called somatostatin receptor scintigraphy. This test uses radioactive tracers to help locate tumors. Other helpful imaging tests include ultrasound, computerized tomography (CT) and magnetic resonance imaging (MRI).