A 48-year-old man has recurrent jejunal ulcers despite proton pump inhibitor therapy. Fasting serum gastrin is 550 pg/mL with gastric pH 2.0. Which dynamic test result best confirms the diagnosis?

• A Rise in serum gastrin after a standard protein meal exceeding 100 percent of baseline
• B Fall in serum gastrin after intravenous calcium infusion
• C Paradoxical rise in serum gastrin after intravenous secretin ✓
• D No change in serum gastrin after intravenous pentagastrin

Explanation

Gastrinoma cells express secretin receptors that are functionally abnormal, so secretin stimulates rather than suppresses gastrin release; a rise above 120 pg/mL over baseline confirms Zollinger-Ellison syndrome when fasting gastrin and pH criteria are met. The meal test distinguishes G cell hyperplasia, where gastrin rises markedly, from gastrinoma where it changes little, killing option A. Calcium infusion increases gastrin in gastrinoma, so B is wrong.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.