<unk>  may be suspected when the above symptoms prove resistant to treatment when the symptoms are especially suggestive of the<unk> , or when endoscopy is suggestive. The diagnosis is made through several laboratory tests and imaging studies: * Secretin stimulation test, which measures evoked gastrin levels. Note that the mechanism underlying this test is in contrast to the normal physiologic mechanism whereby secretin inhibits gastrin release from G cells. Gastrinoma cells release gastrin in response to secretin stimulation, thereby providing a sensitive means of differentiation. * Fasting gastrin levels on at least three occasions * Gastric acid secretion and pH (normal basal gastric acid secretion is less than 10 mEq/hour; in<unk><unk>  patients, it is usually more than 15 mEq/hour) * An increased level of chromogranin A is a common marker of neuroendocrine tumors. In addition, the source of the increased gastrin production must be determined using MRI or somatostatin receptor scintigraphy.
Zollinger–Ellison syndrome
Toriello–Carey syndrome
Naegeli–Franceschetti–Jadassohn syndrome
Johanson–Blizzard syndrome
Meigs's syndrome
Whipple's disease
HIDEA syndrome
Löffler's syndrome