Gastrin and Pepsinogen: The Stomach Markers Your Routine Bloods Don't Check
When we talk about gut health, most of the attention goes to the microbiome. The stomach gets far less airtime, yet it's where digestion really begins. If it isn't producing enough acid and digestive enzymes, problems can ripple all the way down the gut and show up as symptoms that seem unrelated.
In clinic, I regularly see clients with persistent bloating, reflux, low B12 or iron that won't budge despite supplements. Their standard blood tests usually look fine. Very few have ever had their stomach function checked.
Two markers can help fill that gap: gastrin and pepsinogen. Here's what they are, what they can reveal, and who might benefit from testing.
What Are Gastrin and Pepsinogen?
Your stomach has two main working areas, and each one produces something we can measure in the blood.
The upper body of the stomach (the corpus) makes stomach acid and pepsinogen I. Pepsinogen is the inactive form of pepsin, the enzyme that starts breaking down protein. Stomach acid switches it on. A second type, pepsinogen II, is made more widely across the stomach lining.
The lower part of the stomach (the antrum) makes gastrin-17, a hormone that tells the stomach to produce acid. When acid levels are low, gastrin rises to push production up. When acid is plentiful, gastrin falls.
So these markers work as a feedback system. Read together, they tell us whether each part of the stomach is healthy and whether it's producing the acid it should.
Why stomach acid matters
Stomach acid has a bad reputation thanks to reflux, but you need it. It:
Activates pepsin to digest protein
Releases B12, iron, calcium and zinc from food so they can be absorbed
Kills bacteria and other microbes that arrive with your meals
Signals the pancreas and gallbladder to release enzymes and bile further down
Low acid can therefore play a part in nutrient deficiencies, bloating after protein-rich meals, and bacterial overgrowth such as SIBO.
What the results can reveal
These markers are usually tested together, often alongside H. pylori antibodies, in a stomach panel such as GastroPanel. The pattern matters more than any single number.
Pattern | What it can suggest |
Low pepsinogen I, low pepsinogen I/II ratio, high gastrin-17 | The acid-producing upper stomach lining may be thinning (atrophic gastritis of the corpus), so acid output is low and gastrin rises to compensate |
Low gastrin-17 with normal pepsinogens | Possible changes in the lower stomach (antrum), or simply high acid output |
Raised pepsinogens and positive H. pylori antibodies | Active or past H. pylori infection, with inflammation of the stomach lining |
All within range, H. pylori negative | A healthy, functioning stomach lining |
Atrophic gastritis: the quiet one
Atrophic gastritis means the stomach lining has gradually lost some of its glands. It's often caused by long-term H. pylori infection or by autoimmunity, where the immune system attacks the acid-producing cells. It frequently causes no obvious symptoms at all.
That matters because it can lead to poor absorption of B12, iron, folate and calcium. It's also a recognised risk factor for stomach cancer, which is why a result suggesting atrophy should always be followed up with your GP, who may refer you for a gastroscopy.
A note on acid-reducing medication
Proton pump inhibitors (PPIs) such as omeprazole and lansoprazole reduce stomach acid. In response, gastrin rises, and pepsinogen levels can increase too. That's an expected effect of the medication and needs to be factored into how results are read.
Please don't stop a prescribed PPI to get a "cleaner" result. If you're on one, tell your practitioner and talk to your GP before changing anything.
Who might benefit from testing?
I'd consider looking at stomach function if you have:
Low B12 or iron that keeps coming back, or doesn't improve with supplements
Bloating or heaviness after meals, especially protein
Reflux or indigestion, particularly if you've been on acid-reducing medication for a long time
Recurring SIBO
An autoimmune condition such as thyroid disease, coeliac disease or type 1 diabetes, since autoimmune gastritis often travels with these
A history of H. pylori infection
A family history of stomach cancer or pernicious anaemia
These markers are a screening tool and don't replace a diagnosis. A result is one piece of the picture, read alongside your symptoms, history and other tests. Anything that points towards atrophy or infection goes back to your GP.
What helps
Support always depends on what the results show, which is exactly why testing beats guessing. Depending on the picture, that might include:
Addressing H. pylori with your GP if it's active
Correcting B12, iron and other deficiencies, sometimes in forms that don't depend on stomach acid
Eating slowly, chewing well and keeping meals calm, since digestion starts in a relaxed nervous system
Bitter foods such as rocket, chicory and radicchio before meals to support digestive secretions
Targeted digestive support where appropriate, which I'd only recommend once we know what's going on
The bottom line
If your gut symptoms or deficiencies keep returning however carefully you eat, it's worth looking further up the digestive tract. Your stomach sets the conditions for everything that follows, and gastrin and pepsinogen offer a simple, non-invasive way to see how it's working.
As a Functional Medicine Practitioner and Nutritional Therapist, I use functional testing to understand what's driving your symptoms, then build a plan around the results. If you'd like to explore whether stomach testing makes sense for you, book a free discovery call.
Functional medicine and nutritional therapy offer educational support and personalised guidance. They do not diagnose, treat or cure medical conditions and are not a substitute for medical advice.
Comments