Gastrin Level Evaluation and Clinical Indications

Primary Clinical Indications for Gastrin Testing

The American Gastroenterological Association recommends measuring gastrin levels in patients with high-volume watery diarrhea (>1 liter/day) with dehydration and hypokalemia when other causes have been excluded 3
The National Comprehensive Cancer Network recommends measuring gastrin levels in patients with severe or recurrent peptic ulcers, particularly those located in unusual anatomical locations (beyond the duodenal bulb, in the descending duodenum or jejunum), multiple ulcers, or ulcers refractory to standard therapy 4
Gastrin levels should be measured in patients with recurrent peptic ulcer disease with gastrointestinal bleeding in the absence of H. pylori infection, as recommended by the European Society of Gastrointestinal Endoscopy 1
The American College of Gastroenterology recommends evaluating patients with suspected MEN-1 syndrome for gastrinoma, as all gastrinoma patients should be evaluated for MEN-1 1

Fasting serum gastrin >1000 pg/mL combined with gastric pH <2 is diagnostic of gastrinoma, according to the National Comprehensive Cancer Network 4
Normal gastrin levels are approximately 150 pg/mL, with gastrinoma patients averaging around 1000 pg/mL, as reported by the European Society of Gastrointestinal Endoscopy 3
The American Gastroenterological Association notes that comparable elevations in gastrin levels occur in pernicious anemia, atrophic gastritis, and with proton pump inhibitor therapy 3

Proton pump inhibitors (PPIs) and H2 antagonists elevate both gastrin and chromogranin A levels, according to the European Society of Gastrointestinal Endoscopy 1
The American College of Gastroenterology recommends withdrawing PPIs with great caution and ideally stopping them 10-14 days before measuring fasting gastrin 1

Gastric pH is the key discriminator between NET types, as reported by the National Comprehensive Cancer Network 6
Type 1 gastric NETs (70-80% of gastric NETs) are characterized by pH >4-5, indicating achlorhydria from atrophic gastritis with physiologic hypergastrinemia from parietal cell loss 6
Type 2 gastric NETs are characterized by pH <2, indicating gastrinoma/Zollinger-Ellison syndrome 6
Type 3 gastric NETs are characterized by normal gastrin levels 1

Raised gastrin levels also occur in renal insufficiency, a common cause that must be ruled out before pursuing ZES diagnosis, as noted by the American Society of Nephrology 2
The European Society of Gastrointestinal Endoscopy reports that raised gastrin levels also occur in diabetes mellitus and rheumatoid arthritis 3

When gastrin is elevated but <10 times normal with gastric pH <2, the American Gastroenterological Association recommends documenting increased basal acid output (BAO), with BAO >15 mmol/h indicative of gastrinoma in the presence of raised serum gastrin 3
The National Comprehensive Cancer Network recommends calculating the BAO/MAO ratio, with a ratio >0.6 highly specific for gastrinoma 3
The European Society of Gastrointestinal Endoscopy notes that a secretin stimulation test may be necessary in equivocal cases 3