Confirming a Diagnosis of Zollinger-Ellison Syndrome

Zollinger-Ellison Syndrome (ZES) is a rare condition that occurs when one or more tumors, called gastrinomas, form in your pancreas or the upper part of your small intestine (duodenum) ^[1]. These tumors release large amounts of a hormone called gastrin, which signals your stomach to produce excessive amounts of acid ^[2]. This excess acid leads to severe peptic ulcers and chronic diarrhea.

Diagnosing ZES is often a complex process because its symptoms overlap with much more common issues like standard acid reflux (GERD) or typical stomach ulcers ^[2]. On average, patients experience symptoms for more than five years before receiving a correct diagnosis ^[2].

The Biochemical Diagnostic Pattern

Because many conditions and medications can cause high gastrin levels, a diagnosis of ZES cannot be made based on a blood test alone ^[3]. Doctors typically look for a specific confirmatory pattern combining two factors:

1. Elevated Fasting Serum Gastrin (FSG): Your gastrin levels must be significantly elevated after fasting overnight. A level above 1,000 pg/mL (or greater than 10 times the upper limit of normal) is strongly supportive of ZES ^[1]. However, many patients have lower elevations, which require expert evaluation to interpret.
2. Gastric pH < 2.0: This measurement, typically taken during an endoscopy or via a specialized probe, proves that your stomach is highly acidic ^[1].

If your gastrin is high but your stomach acid is low (a high pH), ZES is unlikely, provided the measurement is valid ^[3]. Low stomach acid actually triggers the body to produce more gastrin to try and fix the balance—this is a normal response seen in conditions like atrophic gastritis or when taking acid-blocking medications ^[3][4]. True ZES is “inappropriate” high gastrin: the body keeps pumping out the hormone even though the stomach is already dangerously acidic ^[3].

The Secretin Stimulation Test

In cases where gastrin levels are elevated but the diagnosis is equivocal, doctors may use the secretin stimulation test ^[1].

Under normal circumstances, a hormone called secretin tells the stomach to stop producing gastrin. However, gastrinoma cells behave abnormally—they react to secretin by releasing even more gastrin into your bloodstream ^[1][5]. During this test, a medical professional will give you an intravenous (IV) dose of secretin and draw blood at specific intervals to see if your gastrin levels spike ^[1].

What the Test Day Involves: You will be asked to fast overnight. A nurse will place an IV line to administer the secretin and draw several blood samples over roughly 30 to 60 minutes. Your specialist will give you exact instructions on whether to take your acid-blocking medications that morning.

The Danger of Stopping PPIs

Proton pump inhibitors (PPIs) like omeprazole, lansoprazole, and pantoprazole are the standard treatment for high stomach acid. However, they complicate the diagnostic process because they naturally raise gastrin levels and lower stomach acid (raising pH) ^[6][7].

While older protocols suggested stopping PPIs for at least one week before testing, this can be extremely dangerous for someone with suspected ZES ^[6]. Abruptly stopping these medications can cause recurrent acid hypersecretion, leading to rapid return of severe ulcers, gastrointestinal bleeding, or perforation (a hole in the stomach or intestine) ^[6][7][8].

Important Safety Note: Never stop or change your PPI dose on your own. Medication management before testing must be decided by an experienced gastroenterologist or neuroendocrine-tumor center. Some centers have validated protocols to perform secretin stimulation tests while you stay on your PPI medication, while others may carefully transition you to an alternative medication (like an H2 blocker) with close monitoring ^[9].

Why Diagnosis Takes Time

The delay in diagnosing ZES usually happens because the symptoms are so common ^[2]. ZES is typically only suspected when:

• Ulcers are unusually severe or keep coming back despite high-dose treatment ^[2].
• You have multiple ulcers in unusual locations ^[2].
• You have severe diarrhea that improves when taking acid blockers ^[2].
• You have a family history of Multiple Endocrine Neoplasia type 1 (MEN1) ^[6][10].

If ZES is suspected, your care team will use a combination of these blood and acid tests, followed by specialized imaging to locate the small tumors ^[10].