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PubMed This is a summary of 19 peer-reviewed journal articles Updated
Gastroenterology

Understanding Autoimmune Gastritis

At a Glance

Autoimmune Gastritis (AIG) is an underdiagnosed condition where the immune system attacks the stomach lining. This stops the body from absorbing iron and Vitamin B12, causing hidden symptoms like severe fatigue, brain fog, and anemia long before digestive issues appear.

If you have been feeling “off” for years—struggling with crushing fatigue, brain fog, or digestive issues that no one could explain—learning you have Autoimmune Gastritis (AIG) can be a profound turning point. It is often a moment of deep relief to finally have a name for your experience [1].

AIG is a chronic condition where your immune system mistakenly identifies the cells in your stomach lining as “foreign” and begins to attack them [2]. While it has historically been viewed as a rare disease, experts now believe it is significantly underdiagnosed [1][3]. Because the symptoms can be subtle and range from stomach upset to neurological changes, many patients spend years visiting different specialists before the pieces of the puzzle finally click together [4][1].

The Biology of the Attack

The primary targets of this immune attack are the parietal cells [2]. These specialized cells live in the lining of your stomach and have two critical jobs:

  1. Producing Stomach Acid: They use a “proton pump” (the H+/K±ATPase enzyme) to create the acid needed to break down food and kill harmful bacteria [5][6].
  2. Creating Intrinsic Factor: This is a vital protein that acts like a “key” to unlock Vitamin B12 from your food so your body can absorb it later in the digestive tract [7][8].

In AIG, your immune system produces anti-parietal cell antibodies (APCA) that damage these cells [9][10]. As the parietal cells are lost, the stomach environment changes from acidic to non-acidic, a state called hypochlorhydria [2][6]. Without enough acid and intrinsic factor, your body loses its ability to properly absorb essential nutrients like iron and Vitamin B12 [11][7].

The Road to Diagnosis

For many, the clinical journey starts not with stomach pain, but with the side effects of nutrient deficiencies. This is why AIG is so frequently missed in its early stages [1].

  • The Iron Warning Sign: Often, the first clue is refractory iron deficiency anemia—low iron that does not improve even when you take iron supplements [12][11].
  • The B12 Connection: As the disease progresses, the lack of intrinsic factor leads to Vitamin B12 deficiency, which can cause pernicious anemia and neurological symptoms like “brain fog,” tingling in the hands and feet, or balance issues [7][8].
  • Digestive Symptoms: You may experience dyspepsia (indigestion), bloating, or a feeling of fullness very quickly after eating [13][14].

Because these symptoms are common to many other conditions, doctors may first look for more “obvious” causes. It is common for patients to be told their fatigue is just stress, or their iron deficiency is simply due to diet [1][4].

Why It Often Goes Undetected

AIG is considered underdiagnosed for several reasons. First, the damage to the stomach lining can be “patchy” or subtle, meaning it might be missed during a standard endoscopy (a procedure where a camera is used to look inside the stomach) if specific biopsies are not taken [15][16]. Second, a common stomach infection called Helicobacter pylori can mimic or even hide the signs of AIG, leading doctors to treat the infection while the underlying autoimmune process continues unnoticed [17][18].

Current medical guidelines now emphasize that when a patient has unexplained B12 or iron deficiencies, doctors should use specific blood tests to look for markers of AIG, such as gastrin levels and pepsinogen ratios [10][19]. Understanding that your symptoms have a physical, biological cause is the first step toward managing the condition and reclaiming your health.

Common questions in this guide

What are the first signs of Autoimmune Gastritis?
Often, the first signs of Autoimmune Gastritis are not stomach problems, but symptoms of nutrient deficiencies. These can include severe fatigue, brain fog, or iron deficiency anemia that does not improve even when you take iron supplements.
How does Autoimmune Gastritis affect Vitamin B12 and iron absorption?
The condition damages parietal cells in the stomach, which are responsible for producing stomach acid and a protein called intrinsic factor. Without enough stomach acid and intrinsic factor, your body loses its ability to properly unlock and absorb iron and Vitamin B12 from your food.
Why is Autoimmune Gastritis so hard to diagnose?
AIG is frequently missed because its symptoms, like fatigue and indigestion, overlap with many common conditions. Additionally, the damage to the stomach lining can be patchy and hard to see during a standard endoscopy if specific biopsies aren't taken.
What tests are used to diagnose Autoimmune Gastritis?
Doctors use specific blood tests to look for markers like anti-parietal cell antibodies, gastrin levels, and pepsinogen ratios. They may also perform an endoscopy with targeted biopsies to identify microscopic damage to the stomach lining.
Do I need regular screenings if I have Autoimmune Gastritis?
Yes, people with Autoimmune Gastritis may need periodic endoscopies to monitor the health of their stomach lining. Your doctor will use these screenings to check for the progression of stomach atrophy and monitor for neuroendocrine tumors or other changes.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is the current stage of my stomach lining (atrophy), and how does that affect my long-term care?
  2. 2.Have we checked both my Vitamin B12 and iron (ferritin) levels recently, and are they in the optimal range?
  3. 3.Based on my diagnosis, do I need regular screenings (endoscopies) to monitor for neuroendocrine tumors or other changes?
  4. 4.Since AIG is linked to other autoimmune conditions, should we screen for thyroid issues or Type 1 diabetes?
  5. 5.If I have low stomach acid, are there specific foods or medications I should avoid?

Questions For You

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Related questions

Is Autoimmune Gastritis Deadly? Risks & Life ExpectancyWhat Is the Best Diet for Autoimmune Gastritis (AIG)?What is the Prognosis for Autoimmune Gastritis?

References

References (19)
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    Determinants of diagnostic delay in autoimmune atrophic gastritis.

    Lenti MV, Miceli E, Cococcia S, et al.

    Alimentary pharmacology & therapeutics 2019; (50(2)):167-175 doi:10.1111/apt.15317.

    PMID: 31115910
  2. 2

    Natural history of autoimmune atrophic gastritis: a prospective, single centre, long-term experience.

    Miceli E, Vanoli A, Lenti MV, et al.

    Alimentary pharmacology & therapeutics 2019; (50(11-12)):1172-1180 doi:10.1111/apt.15540.

    PMID: 31621927
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    High incidence of autoimmune gastritis in patients misdiagnosed with two or more failures of H. pylori eradication.

    Furuta T, Baba S, Yamade M, et al.

    Alimentary pharmacology & therapeutics 2018; (48(3)):370-377 doi:10.1111/apt.14849.

    PMID: 29920721
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    Autoimmune Gastritis and Hypochlorhydria: Known Concepts from a New Perspective.

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    International journal of molecular sciences 2024; (25(13)) doi:10.3390/ijms25136818.

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    Measurement of Autoantibodies to Gastric H+,K+-ATPase (ATP4A/B) Using a Luciferase Immunoprecipitation System (LIPS).

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    Methods in molecular biology (Clifton, N.J.) 2019; (1901()):113-131 doi:10.1007/978-1-4939-8949-2_10.

    PMID: 30539573
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    Creating a Framework for Treating Autoimmune Gastritis-The Case for Replacing Lost Acid.

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    Nutrients 2024; (16(5)) doi:10.3390/nu16050662.

    PMID: 38474790
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    A case report: subacute combined degeneration of the spinal cord and pernicious anemia caused by autoimmune gastritis.

    Sun Z, Yu X

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    PMID: 35777065
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    Type-1 Grade 2 Multi-Focal Gastric Neuroendocrine Tumors Secondary to Chronic Autoimmune Gastritis.

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    Validation of diagnostic strategies of autoimmune atrophic gastritis: A case report.

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    Relevance of pepsinogen, gastrin, and endoscopic atrophy in the diagnosis of autoimmune gastritis.

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    Autoimmune Gastritis in Children: A Rare Cause of Refractory Iron-Deficiency Anemia.

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    Use of the Wireless Motility Capsule in the Diagnosis of Gastric Hypochlorhydria: pHinding Extra Value.

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    Assessment of Gastric Emptying in Patients with Autoimmune Gastritis.

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    Helicobacter pylori Gastritis as an Initial Presentation of Evolving Autoimmune Gastritis: A Report of Two Cases.

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This page provides educational information about Autoimmune Gastritis (AIG) and its symptoms. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your doctor for medical advice.

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