A 48-year-old woman from Mumbai with a 3-year history of refractory peptic ulcer disease is referred for investigation. She has failed two courses of triple therapy for H. pylori and remains symptomatic despite continuous omeprazole 40 mg daily. Repeat endoscopy shows a large (3 cm) duodenal ulcer with surrounding edema. H. pylori rapid urease test is negative. Serum gastrin level is 650 pg/mL (normal <100). What is the most appropriate next step in management?

Explanation

## Clinical Context This patient presents with **refractory peptic ulcer disease** (failure of two H. pylori eradication attempts, persistent symptoms despite high-dose PPI). Notably, H. pylori is now negative, and **fasting serum gastrin is elevated at 650 pg/mL** — this is a red flag for **Zollinger-Ellison syndrome (ZES)**. ## Diagnostic Algorithm for Refractory Ulcer + Elevated Gastrin ```mermaid flowchart TD A[Refractory peptic ulcer]:::outcome --> B{H. pylori status?}:::decision B -->|Positive| C[Optimize eradication therapy]:::action B -->|Negative| D{Fasting gastrin?}:::decision D -->|<100 pg/mL| E[Continue PPI; investigate other causes]:::action D -->|100-1000 pg/mL| F[Perform secretin stimulation test]:::action D -->|>1000 pg/mL| G[Likely ZES; imaging for gastrinoma]:::action F --> H{Gastrin rise >200 pg/mL?}:::decision H -->|Yes| I[Confirm ZES diagnosis]:::outcome H -->|No| J[Exclude pseudo-ZES]:::outcome ``` **Key Point:** Elevated fasting gastrin (650 pg/mL) in a patient with refractory ulcer and negative H. pylori is **highly suspicious for Zollinger-Ellison syndrome**. The next diagnostic step is **secretin stimulation test**, which is the gold standard confirmatory test. ## Secretin Stimulation Test: Mechanism & Interpretation **High-Yield:** In ZES, secretin paradoxically **increases** gastrin levels (>200 pg/mL rise from baseline), whereas in normal individuals and G-cell hyperplasia, gastrin is suppressed or unchanged. | Condition | Fasting Gastrin | Secretin Response | Diagnosis | |-----------|-----------------|-------------------|----------| | Normal | <100 | Suppression | Normal | | G-cell hyperplasia | 100–500 | Suppression or ↑ <200 | Benign | | Zollinger-Ellison syndrome | >1000 (often >500) | **↑ >200 pg/mL** | **Gastrinoma present** | | Pseudo-ZES (achlorhydria) | >1000 | Suppression | Atrophic gastritis | **Clinical Pearl:** The secretin stimulation test is the **most sensitive and specific** test to confirm ZES. A paradoxical rise in gastrin >200 pg/mL above baseline after secretin IV bolus (2 units/kg) is diagnostic. ## Why Secretin Stimulation Comes Before Imaging **Tip:** Always confirm ZES biochemically BEFORE imaging for gastrinoma. This prevents unnecessary imaging in false-positive cases (e.g., pseudo-ZES from achlorhydria). Once ZES is confirmed, proceed to CT/MRI abdomen and somatostatin receptor scintigraphy (SRS) to localize the tumor. **Warning:** Do NOT jump directly to imaging or surgery without biochemical confirmation. Secretin stimulation is the gatekeeper test.