From the Guidelines
Positive parietal cell antibodies are a sensitive serum biomarker for autoimmune gastritis (AIG), and patients with this finding should be evaluated for vitamin B12 deficiency and monitored for iron deficiency and increased risk of gastric cancer and carcinoid tumors. This is based on the most recent evidence from a 2021 study published in Gastroenterology, which highlights the importance of checking parietal cell antibodies (PCAs) and intrinsic factor antibodies (IFA) in patients with histology compatible with AIG 1. The presence of PCAs indicates the presence of autoantibodies targeting the proton pump (H+/K+ ATPase) in gastric parietal cells, which is commonly associated with autoimmune gastritis and pernicious anemia.
Some key points to consider in patients with positive parietal cell antibodies include:
- Evaluation for vitamin B12 deficiency through serum B12 levels, methylmalonic acid, and homocysteine testing
- Treatment of B12 deficiency with vitamin B12 supplementation, initially with intramuscular injections (1000 mcg cyanocobalamin or hydroxocobalamin) daily or weekly for several weeks, followed by monthly maintenance injections or high-dose oral supplementation (1000-2000 mcg daily)
- Monitoring for iron deficiency
- Endoscopic surveillance due to increased risk of gastric cancer and carcinoid tumors
- The development of parietal cell antibodies is due to the immune system mistakenly attacking parietal cells, leading to decreased intrinsic factor production, which is essential for B12 absorption in the terminal ileum, as noted in the study 1.
It is essential to note that while parietal cell antibodies are sensitive (present in 80-90% of autoimmune gastritis cases), they are not highly specific, as they can be found in other autoimmune conditions and in up to 10% of healthy older adults, highlighting the need for careful interpretation of test results in the context of clinical presentation and other diagnostic findings 1.
From the Research
Positive Parietal Cell Antibody
- The presence of anti-parietal cell antibodies (APCA) is an indicator of autoimmune atrophic gastritis (AAG) and pernicious anemia (PA) 2.
- APCA can be detected in 85-90% of patients with PA, but their presence is not sufficient for diagnosis as they are also found in other diseases 2.
- APCA are more prevalent in patients with type 1 diabetes, autoimmune thyroid diseases, vitiligo, and celiac disease, and these individuals should be closely screened for AAG/PA 2.
- The presence of APCA is not fully understood in relation to Helicobacter pylori infection, but APCA are found in up to 20.7% of patients with H. pylori infection 2.
Diagnosis and Treatment
- Pernicious anemia is often diagnosed based on the presence of classical immune gastritis and anti-intrinsic factor and/or antiparietal cell antibodies 3.
- Oral vitamin B12 supplementation is an effective treatment for pernicious anemia, with a dosage of 1000 μg/d shown to improve vitamin B12 deficiency in PA patients 3, 4, 5.
- Oral replacement therapy should be the first stage in the treatment of vitamin B12 deficiency, and parenteral vitamin B12 treatment should be considered for patients who do not respond to oral replacement therapy 4.
Prevalence and Associations
- APCA positivity was found in 18.5% of patients with vitamin B12 deficiency, and AIFA positivity was found in 2.3% of patients 4.
- Atrophy was determined endoscopically in 24.5% of patients and pathologically in 41.7% of patients with vitamin B12 deficiency 4.
- Helicobacter pylori positivity was found in 90.7% of patients with vitamin B12 deficiency, but no correlation was found between H. pylori and atrophy 4.