Which diagnostic study is preferred for evaluating Zollinger-Ellison syndrome?

The preferred diagnostic study for evaluating Zollinger-Ellison syndrome is the measurement of gastrin levels. This condition is characterized by gastrin-secreting tumors (gastrinomas) that lead to excessive gastric acid production, resulting in recurrent peptic ulcers and other gastrointestinal symptoms.

Determining gastrin levels helps in diagnosing Zollinger-Ellison syndrome, as elevated levels are indicative of the disease. A fasting serum gastrin level is typically measured, and levels greater than a certain threshold (usually above 1000 pg/mL) are suggestive of gastrinoma, especially when coupled with low gastric pH.

Other diagnostic tests may be useful in the evaluation of different conditions but are not specific for Zollinger-Ellison syndrome. For example, the D-xylose absorption test is used to assess intestinal absorption and is not relevant to gastrinomas. The 5-HIAA assay measures serotonin metabolism and is used in diagnosing carcinoid tumors. The urea breath test is employed to detect Helicobacter pylori infection, which is unrelated to gastrin levels or Zollinger-Ellison syndrome directly.