What this test measures
Gastrin is a peptide hormone secreted by G cells in the stomach antrum. It stimulates parietal cells to produce gastric acid and supports gastric mucosal growth. Gastrin release is normally suppressed when stomach pH falls below 3 — a feedback loop that keeps acid output controlled.
Fasting serum gastrin is the first-line laboratory test for gastrinoma (a rare neuroendocrine tumour causing severe, refractory peptic ulcer disease — Zollinger-Ellison syndrome) and for pernicious anaemia (autoimmune atrophic gastritis with low acid and very high compensatory gastrin).
Why it matters
In India, peptic ulcer disease is mostly due to H. pylori, NSAID use and stress — gastrinoma is rare but missed cases account for a small fraction of refractory or recurrent ulcers, especially when ulcers are multiple, distal in the duodenum, or accompanied by diarrhoea. Long-term proton pump inhibitor (PPI) use — extremely common in India for vague dyspepsia — also raises gastrin, often making interpretation difficult.
Gastrin is also useful in pernicious anaemia (where it is markedly raised), which is increasingly recognised as a cause of B-12 deficiency in older Indian adults.
How to prepare
Fasting for 12 hours (overnight) is essential — food strongly raises gastrin. Stop proton pump inhibitors (PPIs) for 1–2 weeks and H2 blockers for 24 hours before the test if safe to do so — only stop under medical guidance. Mention all medications. Do not chew gum or smoke before the test.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Gastrin (Fasting) (pg/mL)[1][2] | < 100 (fasting; varies by lab — confirm reference) | Low gastrin is not common and not generally concerning. Can be seen with antrectomy (surgical removal of the gastrin-producing stomach segment). | Mild rise (100–500 pg/mL) — most often PPI use (very common), H. pylori infection, chronic kidney disease, or mild atrophic gastritis. Significant rise (500–1000) — atrophic gastritis / pernicious anaemia, chronic PPI use, post-vagotomy. Very high (>1000) — pernicious anaemia or gastrinoma (Zollinger-Ellison syndrome). A secretin stimulation test is used to confirm gastrinoma when values are equivocal. |
Causes of a raised fasting gastrin
| Gastrin level (pg/mL) | Likely cause | Distinguishing feature |
|---|---|---|
| 100 – 500 | PPI use, H. pylori, mild atrophic gastritis | Stop PPI 2 weeks → retest; H. pylori serology / urea breath test |
| 500 – 1000 | Atrophic gastritis, pernicious anaemia, long-term PPI | Low B-12, raised parietal cell / intrinsic factor antibodies |
| > 1000 with gastric pH < 2 | Gastrinoma (Zollinger-Ellison) | Severe / multiple ulcers, diarrhoea — secretin stimulation test + imaging |
| > 1000 with high gastric pH | Pernicious anaemia, atrophic gastritis | Low B-12, intrinsic factor antibodies |
Frequently asked questions
Why do I need to fast for a gastrin test?
Food strongly stimulates gastrin — a non-fasting sample can be 2–3 times higher than a fasting one and is uninterpretable. Fast overnight (10–12 hours) and have the sample drawn first thing in the morning.
I take a PPI — do I need to stop before the test?
Ideally yes — PPIs raise gastrin substantially and can mimic a gastrinoma. Stop PPIs for 1–2 weeks and H2 blockers for 24 hours before testing, but only with your doctor's guidance (and bridge with antacids or sucralfate if needed).
What is Zollinger-Ellison syndrome?
A rare neuroendocrine tumour (gastrinoma) — usually in the pancreas or duodenum — that produces excess gastrin, causing severe acid output, multiple recurrent peptic ulcers, and watery diarrhoea. Diagnosed with high fasting gastrin (>1000), low gastric pH, and a positive secretin stimulation test.
Can H. pylori raise gastrin?
Yes — H. pylori infection commonly causes mild gastrin elevation that returns to normal after eradication.
How is gastrin used in pernicious anaemia?
In pernicious anaemia, the immune system destroys acid-producing parietal cells. Low acid removes the feedback signal, so the antrum keeps producing gastrin — values are often very high. Combined with low B-12, raised parietal cell / intrinsic factor antibodies and macrocytic anaemia, it confirms the diagnosis.
How is gastrinoma confirmed?
Beyond a high fasting gastrin and low gastric pH, a secretin stimulation test (which paradoxically raises gastrin in gastrinoma) is the gold-standard biochemical test. Imaging — endoscopic ultrasound, somatostatin receptor PET (Ga-68 DOTATATE) and CT — localises the tumour.
Are gastrinomas always cancerous?
Most gastrinomas have malignant potential, though many are slow-growing. About 25% are part of MEN-1 (multiple endocrine neoplasia type 1), which also includes parathyroid and pituitary tumours.
Related Liver / Enzymes tests
Tests commonly ordered alongside GASTRIN, or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — Gastrin Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Gastrinoma · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Laboratories — Gastrin, Serum · accessed 2026-05-30T00:00:00.000Z
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