What test is considered gold standard for Zollinger-Ellison Syndrome?

• A. EGD
• B. Fasting [gastrin] level
• C. Secretin Challenge Test
• D. Somatostatin Receptor Scintigraphy

Answer: (D)

Somatostatin receptor scintigraphy is used to localize gastrin-secreting tumors because these tumors often express somatostatin receptors. The test uses radiolabeled octreotide, which binds to those receptors and allows whole-body imaging to identify both primary gastrinomas (often in the pancreas or duodenum) and metastatic sites. This makes it highly effective for locating the tumor and guiding surgical or therapeutic planning.

Other options don’t serve localization well. Endoscopy visualizes mucosa but doesn’t reach pancreatic or duodenal tumors. A fasting gastrin level is a screening test and can be elevated for reasons other than gastrinoma, so it doesn’t pinpoint where the tumor is. A secretin stimulation test helps confirm a gastrinoma once biochemical evidence exists, but it doesn’t map tumor location.