Zollinger Ellison Syndrome is diagnosed if serum gastrin level is greater than:

The diagnosis of ZES is made by measuring the serum gastrin level. It is impoant that patients stop taking proton pump inhibitors for this test. In most patients with gastrinomas, the level is >1000 pg/mL. Gastrin levels can be elevated in conditions other than ZES. Common causes of hypergastrinemia include pernicious anemia, treatment with proton pump inhibitors, renal failure, G-cell hyperplasia, atrophic gastritis, retained or excluded antrum, and gastric outlet obstruction. In equivocal cases, when the gastrin level is not markedly elevated, a secretin stimulation test is helpful. Ref: Schwaz's principle of surgery 9th edition, chapter 33.