<prompt> Zollinger Ellison Syndrome is diagnosed if serum gastrin level is greater than:100 pgml500 pgml1000 pgml5000 pgml  <response>: 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 pgmL. 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: Schwazs principle of surgery 9th edition, chapter 33. 