In a 43-year-old woman with a normal upper gastrointestinal endoscopy and a mildly elevated fasting gastrin level, could this represent Zollinger‑Ellison syndrome?

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Last updated: September 23, 2026 • View editorial policy

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Can a Normal Upper GI Endoscopy Rule Out Zollinger-Ellison Syndrome?

No, a normal upper gastrointestinal endoscopy does NOT exclude Zollinger-Ellison syndrome (ZES), particularly in a patient with mildly elevated fasting gastrin levels. The diagnosis of ZES depends primarily on biochemical confirmation and tumor localization through specialized imaging, not endoscopic findings.

Why Endoscopy Can Be Normal in ZES

The most recent 2025 MEN1 guidelines emphasize that gastrinomas in the duodenum are often extremely small (several millimeters in size) and can easily be missed on standard endoscopy 1. Even when present, these tiny tumors may not produce visible mucosal abnormalities that would be detected during routine upper endoscopy.

Key Diagnostic Considerations

Traditional diagnostic criteria require:

  • Fasting gastrin level elevated ≥10-fold above upper limit of normal
  • Gastric pH ≤2 (indicating acid hypersecretion)
  • Absence of proton pump inhibitor (PPI) use 2

However, the 2025 guidelines acknowledge this approach is increasingly problematic in real-world practice 1.

The Challenge with Mildly Elevated Gastrin

Your patient's scenario—normal endoscopy with mildly elevated gastrin—represents a particularly challenging diagnostic situation that the most recent guidelines specifically address:

Alternative Diagnostic Approach (2025 Guidelines)

Given the widespread PPI use and risks of stopping these medications, alternative diagnostic criteria now include 1:

  • Characteristic symptoms (refractory reflux, peptic ulcers, diarrhea)
  • Elevated fasting serum gastrin (even if <10-fold elevation)
  • Presence of duodenopancreatic neuroendocrine tumor on imaging
  • Positive somatostatin receptor scintigraphy (or positive gastrin staining on biopsy)

Critical point: The guidelines note that prospectively screened or early-stage patients "might be asymptomatic but have mild elevations in fasting serum gastrin, which become more prominent with symptoms over time" 1.

Recommended Diagnostic Algorithm

Step 1: Confirm Hypergastrinemia Off PPIs

  • Stop PPIs for at least 1 week (H2 blockers for 48 hours) 2, 3
  • Remeasure fasting gastrin with gastric pH
  • Caution: Most patients with elevated gastrin do NOT have gastrinoma—common causes include PPI use, H. pylori infection, atrophic gastritis, and renal failure 2

Step 2: Provocative Testing

If gastrin is elevated but <10-fold and clinical suspicion remains high:

Secretin stimulation test (first-line provocative test) 2:

  • Administer 4 μg/kg secretin IV over 1 minute
  • Measure gastrin at intervals post-infusion
  • Positive if paradoxical gastrin increase occurs

Important caveat: Historical case reports document ZES with persistently normal fasting gastrin levels where secretin testing was diagnostic 4, 5. This underscores that normal baseline values don't exclude the diagnosis when clinical suspicion is high.

Step 3: Tumor Localization

Even with normal endoscopy, pursue specialized imaging 1:

Primary modalities:

  • Somatostatin receptor scintigraphy-PET (DOTATOC/DOTATATE): Current gold standard for localization with high sensitivity and specificity 1
  • MRI: Excellent for pancreatic lesions
  • Endoscopic ultrasound (EUS): Sensitivity up to 83% for pancreatic gastrinomas, but substantially lower for duodenal lesions 2

Step 4: Consider Repeat Endoscopy with Targeted Approach

The 2025 guidelines specifically recommend: "Patients who are symptomatic should undergo oesophagogastroduodenoscopy, and this is also suggested in all patients with elevated fasting serum gastrin levels to look for signs of Zollinger-Ellison syndrome, a duodenal primary and gastric neuroendocrine tumour" 1.

This means:

  • Look specifically for peptic ulcerations (especially post-bulbar duodenum)
  • Examine for small duodenal lesions
  • Consider EUS if standard endoscopy is unrevealing

Common Pitfalls to Avoid

  1. Measuring gastrin while on PPIs: This is the most common error—PPIs elevate gastrin levels and confound diagnosis 2, 3

  2. Assuming normal endoscopy excludes ZES: Duodenal gastrinomas are frequently only millimeters in size and invisible on standard endoscopy 1

  3. Using unreliable gastrin assays: A 2011 study found that 7 of 12 commercial gastrin assays were inaccurate, leading to false-negative or false-positive results 6. Ensure your laboratory uses a validated assay.

  4. Dismissing mild gastrin elevations: Early or asymptomatic ZES can present with only mild hypergastrinemia 1

  5. Failing to check gastric pH: Hypergastrinemia with achlorhydria (pH >4) suggests atrophic gastritis or PPI effect, not gastrinoma 2

Clinical Bottom Line

In your 43-year-old woman with normal endoscopy and mildly elevated gastrin:

  • Do not dismiss ZES based on normal endoscopy alone
  • Ensure gastrin was measured off PPIs for ≥1 week
  • Measure gastric pH to confirm acid hypersecretion
  • Proceed with secretin stimulation test if clinical suspicion persists
  • Obtain somatostatin receptor PET imaging for tumor localization
  • Consider that 70% of MEN1-associated gastrinomas are duodenal and often microscopic 2, 3

The diagnosis requires a biochemical and imaging-based approach, not reliance on endoscopic visualization of the tumor itself.

References

2
Guideline

neuroendocrine tumors, version 1.2015.

Journal of the National Comprehensive Cancer Network : JNCCN, 2015

3
Guideline

neuroendocrine tumors.

Journal of the National Comprehensive Cancer Network : JNCCN, 2012

Related Questions

Which of the following patients is the most likely candidate for Zollinger‑Ellison syndrome: a 75‑year‑old woman with chronic polyarthritis on long‑term diclofenac therapy and a perforated duodenal ulcer; b 30‑year‑old man with heartburn and abdominal pain, endoscopy showing severe erosive esophagitis, multiple scarred duodenal ulcers, and an acute post‑bulbar ulcer; c 30‑year‑old man admitted for upper gastrointestinal bleeding, endoscopy revealing a duodenal bulb ulcer with adherent clot and a positive urea test from an antral biopsy; d 60‑year‑old man with dyspepsia and diarrhea, a vagotomy performed >20 years ago for duodenal ulcer and elevated serum gastrin; e 25‑year‑old woman with severe heartburn on low‑dose proton‑pump inhibitor therapy, intermittent mild diarrhea, and slightly elevated serum gastrin?
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