Gastrin Unit Converter
Gastrin Unit Converter
Convert fasting gastrin between pg/mL, ng/L and pmol/L. Before reading a raised result: proton pump inhibitors raise gastrin substantially, so a high value in someone taking one is expected rather than diagnostic.
Gastrin converter
Mass ⇄ molarFasting gastrin 40 pg/mL, off acid suppression
The three units, and why the molar figure is approximate
pmol/L = pg/mL × 0.476644
derived from a molecular weight of 2,098 Da for gastrin-17
- pg/mL = ng/L
- a picogram per millilitre and a nanogram per litre are the same concentration, so a report in one reads directly against an interval quoted in the other
- × 0.476644
- the molar factor, from a mass of 2,098 daltons for gastrin-17 — the dominant circulating form in the fasting state
- why it is approximate
- gastrin circulates as a family of peptides, not one molecule. Gastrin-17 predominates in fasting plasma but gastrin-34, gastrin-71, gastrin-14 and partially processed precursors circulate alongside it, at roughly double the mass in the case of gastrin-34. An assay that detects several forms is reporting a mixture, so a molar concentration calculated from a single mass is indicative rather than exact
- assays are not interchangeable
- different commercial assays recognise the various molecular forms to different degrees, which is why published reference intervals and diagnostic thresholds differ between methods and why serial results should come from one laboratory
- the fast is part of the measurement
- gastrin rises after a meal, so an isolated result is only interpretable on a fasting sample — typically overnight, 12 hours or more
Worked example
Fasting gastrin 40 pg/mL, off acid suppression
40 pg/mL = 40 ng/L — the same number in the other mass convention
40 × 0.476644 = 19.07 pmol/L, the molar equivalent for gastrin-17
Against the quoted adult fasting interval of 0–115 pg/mL (0.00–54.81 pmol/L), 40 pg/mL sits within it
That is a meaningful normal result because the patient is off acid suppression. The same 40 pg/mL on a proton pump inhibitor would be unremarkable but far less informative
The molar figure is an approximation: the assay sees gastrin-34 and other forms of different mass alongside gastrin-17
What a fasting gastrin means, and against what
| Fasting gastrin | Gastric pH low (acid present) | Gastric pH high (achlorhydria) |
|---|---|---|
| Normal | Normal physiology | Unexpected — recheck; a normal gastrin with achlorhydria is unusual |
| Modestly raised, roughly 115–400 pg/mL | Consider gastrinoma, retained antrum, gastric outlet obstruction, renal failure — and acid suppression, which must be excluded first | Appropriate response to a high pH: atrophic gastritis, pernicious anaemia, proton pump inhibitor, Helicobacter pylori gastritis, vagotomy |
| Above 1,000 pg/mL | With acid present and a peptic ulcer, taken as diagnostic of gastrinoma | Still usually atrophic gastritis or acid suppression — a very high gastrin with no acid does not indicate a gastrinoma |
Drugs and conditions that raise fasting gastrin
| Cause | Effect | Note |
|---|---|---|
| Proton pump inhibitors | Substantial rise, often above the reference interval | The single commonest reason for a raised gastrin. Mayo advises stopping them for one week before collection where medically feasible |
| H2-receptor antagonists | Smaller rise | Labcorp notes that agents such as cimetidine may elevate gastrin and should be taken into account |
| Atrophic gastritis, pernicious anaemia | Often marked | Loss of parietal cells removes the acid that normally restrains gastrin release |
| Helicobacter pylori infection | Modest rise | Reverses with eradication |
| Chronic kidney disease | Modest rise | Reduced clearance |
| Gastric outlet obstruction, retained gastric antrum after surgery, short bowel | Variable | Structural and post-surgical causes to consider before gastrinoma |
| Gastrinoma (Zollinger–Ellison syndrome) | Usually marked | The diagnosis the test is for, and the least common entry in this table |
Stop the acid suppression first, then read it against the pH
Gastrin is the hormone released by antral G cells that drives gastric acid secretion, and it is measured for one main reason: to look for a gastrinoma, the gastrin-secreting tumour that causes Zollinger–Ellison syndrome. The units are the easy part. Picograms per millilitre and nanograms per litre are the same number, and picomoles per litre is that number multiplied by 0.476644, from a mass of 2,098 daltons for gastrin-17. That molar figure is approximate, because gastrin circulates as a family of peptides — gastrin-17 predominates in the fasting state, but gastrin-34 at roughly twice the mass, gastrin-14, gastrin-71 and partially processed precursors circulate alongside it, and different assays see them to different degrees.
Far more important than any of that is what the patient is taking. Proton pump inhibitors remove the acid that normally restrains gastrin release, and the result is a substantial and entirely expected rise in serum gastrin, frequently above the reference interval. A raised gastrin in someone on omeprazole or its relatives is therefore not a finding; it is the drug. Mayo Clinic Laboratories advises that, where medically feasible, proton pump inhibitors should be stopped for one week before the specimen is collected. That withdrawal is not free of risk in a patient who may genuinely have a gastrinoma, since uncontrolled acid hypersecretion can cause serious complications, so it is a decision for the team investigating rather than something to arrange informally. H2-receptor antagonists raise gastrin less, and the specimen must in any case be fasting, typically after twelve hours or more.
The second requirement is that gastrin is read against gastric acid, not on its own. The feedback loop runs in one direction: as gastric pH rises, gastrin rises to compensate. So a high gastrin in someone with achlorhydria — from atrophic gastritis, pernicious anaemia, or acid suppression — is the stomach behaving exactly as it should, and it can reach striking levels without any tumour being present. The abnormal combination, the one that points to a gastrinoma, is a high gastrin in a patient who is still producing acid. Without a gastric pH or some equivalent evidence of acid secretion, a raised gastrin cannot be assigned to either group.
Where acid secretion is documented, the numbers become useful. Mayo Clinic Laboratories notes that fasting gastrin below 100 pg/mL is seen so uncommonly in untreated gastrinoma as to virtually exclude the diagnosis, that most patients with gastrinoma exceed 400 pg/mL, and that a level above 1,000 pg/mL in a patient with a gastric or duodenal ulcer is considered diagnostic. Values between the reference interval and 400 pg/mL are the difficult zone, and are where the secretin stimulation test and a formal assessment of acid output belong. Reference intervals themselves differ between assays — 0–115 pg/mL and under 100 pg/mL are both in current use by major laboratories — so the interval to trust is the one beside your own result, and serial measurements should stay with one laboratory.
Frequently asked questions
Do proton pump inhibitors affect a gastrin test?
Substantially, and this is the single most important thing about the test. They suppress gastric acid, which removes the feedback that restrains gastrin release, so gastrin rises and frequently exceeds the reference interval. Mayo Clinic Laboratories advises stopping them for one week before collection where medically feasible — a decision to take with the team investigating, since withdrawal carries risk in someone who may have a gastrinoma.
Is pg/mL the same as ng/L for gastrin?
Yes, identical. A picogram per millilitre is a nanogram per litre, so a gastrin of 40 pg/mL is 40 ng/L. To convert to picomoles per litre, multiply by 0.476644, giving 19.07 pmol/L — approximate, because the assay detects several molecular forms of gastrin with different masses.
What gastrin level indicates Zollinger–Ellison syndrome?
Mayo Clinic Laboratories treats a fasting gastrin above 1,000 pg/mL in a patient with a gastric or duodenal ulcer as diagnostic, notes that over 60% of gastrinoma patients exceed 400 pg/mL, and that values below 100 pg/mL virtually exclude it. Those figures assume the patient is off acid suppression and still producing gastric acid.
Why does gastrin need to be interpreted with gastric pH?
Because gastrin rises when gastric acid falls — that is the normal feedback. A high gastrin in someone with achlorhydria from atrophic gastritis, pernicious anaemia or a proton pump inhibitor is an appropriate physiological response, not a tumour. The abnormal pattern is a high gastrin in a patient who is still secreting acid.
Does a gastrin sample have to be fasting?
Yes. Gastrin rises after a meal, so an isolated result is only interpretable on a fasting specimen — reference laboratories specify twelve hours or more, and one asks for twelve to fourteen. A gastrin drawn after eating cannot be compared with any published interval.
Related calculators
References
- Mayo Clinic Laboratories. Test GAST: Gastrin, Serum — reference value <100 pg/mL; guidance to withhold proton pump inhibitors for 1 week before collection; diagnostic thresholds for gastrinoma. Accessed 2026.
- Labcorp. Test 004390: Gastrin — reference interval 0–115 pg/mL for patients older than 16 years after a 12–14 hour fast. Accessed 2026.
- Poitras P, Gingras MH, Rehfeld JF. The Zollinger–Ellison syndrome: dangers and consequences of interrupting antisecretory treatment. Clin Gastroenterol Hepatol. 2012. PMID 21871248.
- Rehfeld JF. Gastrin and the moderate hypergastrinaemias. Int J Mol Sci. 2021;22(13):6977 — on the molecular forms of circulating gastrin and their measurement.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.