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Autoimmune gastritis (AIG) is a chronic and often silent condition that gradually damages the stomach lining and disrupts the body’s ability to absorb essential nutrients—most notably, vitamin B12 and iron. Though it can go undetected for years, AIG may eventually progress to pernicious anaemia (PA) and is associated with serious complications if left untreated. Thanks to advances in serological testing, including EUROIMMUN’s highly specific diagnostics, earlier detection is now more achievable than ever.

What Is Autoimmune Gastritis?

AIG is an immune-mediated inflammation of the gastric mucosa. Over time, this immune attack leads to the destruction of parietal cells, which are responsible for secreting hydrochloric acid, pepsin, and intrinsic factor (IF)—a glycoprotein critical for vitamin B12 absorption. The mucosa becomes infiltrated with lymphocytes, plasma cells and granulocytes. Eventually, necrotic epithelial cells are replaced by mucoid cells, culminating in gastric atrophy.

As this slow degeneration progresses, vitamin B12 deficiency sets in—often unnoticed for years. In later stages, it manifests as pernicious anaemia, with symptoms including:

• Fatigue and drowsiness
• Anaemia and tachycardia
• Neurological disturbances (e.g. paresthesia, memory issues)
• Glossitis, diarrhoea, weight loss and anorexia
• Jaundice due to ineffective erythropoiesis

Vitamin B12 deficiency also impairs DNA synthesis, resulting in the formation of large, immature blood cells (megaloblasts), most commonly observed in bone marrow and the gastrointestinal epithelium.

Serological Markers in Autoimmune Gastritis and PA

Diagnosing AIG and its progression to PA relies heavily on detecting disease-specific autoantibodies, particularly:

1. Parietal Cell Antibodies (APCA)

These autoantibodies target the H⁺/K⁺-ATPase enzyme complex in parietal cells and are primarily of the IgG and IgA classes. Their prevalence is extremely high—nearing 100%—in individuals with chronic atrophic gastritis and newly diagnosed PA. However, APCA can also be found in other autoimmune conditions and even in healthy individuals, particularly the elderly, which underscores the importance of improved specificity in testing.

EUROIMMUN’s innovation
To enhance diagnostic accuracy, EUROIMMUN developed the Anti-ATP4B ELISA (IgG), using the recombinant extracellular domain of the β-subunit of H⁺/K⁺ ATPase (ATP4B) as an antigen. This test offers higher specificity than traditional parietal cell antibody assays without compromising sensitivity.

2. Intrinsic Factor Antibodies (IFA)

These IgG autoantibodies interfere with vitamin B12 absorption in two key ways:

• Type 1 IFA bind to the vitamin B12 binding site on IF, blocking complex formation.
• Type 2 IFA inhibit the binding of IF to its receptor in the ileum, preventing uptake.

IFA are highly specific for AIG and PA, with a diagnostic occurrence in 40–80% of PA patients, depending on disease stage.

Diagnostic Approach

EUROIMMUN offers a comprehensive testing panel for autoimmune gastritis, including:

• Indirect immunofluorescence on monkey stomach tissue to detect APCA
• ELISA tests for intrinsic factor antibodies
• Anti-ATP4B ELISA (IgG) for enhanced specificity in detecting APCA

These assays can be used individually or in combination as part of a broader autoimmune or anaemia work-up, especially for patients presenting with unexplained fatigue, anaemia, neurological symptoms, or signs of malabsorption.

Why Early Detection Matters

Due to its insidious nature, AIG is often overlooked until irreversible damage has occurred. However, early serological screening can support timely diagnosis, allowing clinicians to manage the condition proactively through vitamin B12 supplementation, monitoring for gastric neoplasia and screening for related autoimmune diseases.

AIG is frequently associated with other autoimmune disorders such as:

• Hashimoto’s thyroiditis
• Type 1 diabetes
• Vitiligo
• Addison’s disease

Recognising this connection supports a more comprehensive patient care approach.

Autoimmune gastritis is a slowly progressive but potentially serious autoimmune disorder. Left undetected, it can lead to irreversible vitamin B12 deficiency and pernicious anaemia. With advanced diagnostics like the Anti-ATP4B ELISA and intrinsic factor antibody testing, EUROIMMUN provides clinicians with the tools needed for early and accurate diagnosis—ensuring better outcomes for patients through timely intervention.