Zollinger-Ellison syndrome associated with persistently normal fasting serum gastrin concentrations.

A 63-year-old man with a 2-year history of upper gastrointestinal ulcers was found to have the Zollinger-Ellison syndrome. Despite histologic verification of gastrinoma, several fasting serum gastrin concentrations were normal. However, in response to intravenous secretin infusion, a paradoxical increase in serum gastrin levels indicative of gastrinoma was seen. Although serum gastrin concentrations in patients with suspected gastrinoma may be persistently normal, provocative testing may be necessary to establish the diagnosis of the Zollinger-Ellison syndrome.