Interpretation
Gastrin is typically increased in Zollinger-Ellison syndrome (ZES) from gastrinoma. In 25% of cases, gastrinoma is part of the Multiple Endocrine Neoplasma type 1 (MEN type 1) syndrome.
All patients with confirmed gastrinoma should be evaluated for possible MEN 1 syndrome for which genetic testing is available and may enable cascade screening of other family members.
A fasting serum gastrin concentration > 1000 ng/L, together with a gastric acid pH <=2 is virtually diagnostic of gastrinoma. Around 68% of gastrinoma patients, however have a fasting gastrin concentration up to 1000 ng/L and a small minority (<3%) may have normal fasting gastrin and a stimulation test (secretin or calcium infusion) may be required to support the diagnosis.
Other than gastrinoma, Helicobacter pylori gastritis, pyloric obstruction, post gastric resection with intact antrum and renal failure (which prolongs gastrin excretion) are recognized causes of increased fasting gastrin concentration with gastric pH<=2.
Causes of hypergastrinaemia with gastric pH greater than 2 include chronic atrophic gastritis associated with pernicious anaemia (with low vitamin B12) or chronic Helicobacter pylori infection; post-vagotomy; use of proton pump inhibitor and H2 receptor antagonist therapy. Patients must be off these drugs for at least 1 week for valid interpretation of an elevated gastrin.
If there is strong suspicion of underlying ZES and concern of precipitating peptic ulcer disease, the proton pump inhibitors may be substitued by a H2 receptor antagonist. Fasting gastrin level should then be measured after with-holding oral H2 receptor blocker for 30 hours and intravenous H2 receptor antagonist infusion for 12 hours.
Reference Intervals
<150 normal ng/L
150 – 300 ng/L may be equivocal requiring further tests.
