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Anti-Parietal Cell Antibodies (APCA)

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Anti-Parietal Cell Antibodies (APCA) Test

Anti-parietal cell antibodies (APCA) target H⁺/K⁺-ATPase, an enzyme critical for gastric acid secretion. The autoimmune response is mediated by CD4+ T cells, which attack the H⁺ pump, leading to the destruction of parietal cells in the stomach.

Pathophysiology

  • Damage to parietal cells leads to reduced hydrochloric acid (HCl) secretion, causing hypochlorhydria (low acid) or achlorhydria (complete absence of acid production).
  • This results in malabsorption of essential nutrients, including vitamin B12, due to a deficiency of intrinsic factor (IF), which is necessary for B12 absorption in the intestines.
  • Vitamin B12 deficiency leads to impaired red blood cell formation, causing megaloblastic (pernicious) anemia.
  • Take the test at least 2 hours after the last meal.
  • Avoid smoking for 1 hour before the test.

This test is used to diagnose:

  • Autoimmune megaloblastic (pernicious) anemia
  • Vitamin B12 deficiency and its underlying causes
  • Autoimmune gastritis

A positive APCA test is an early predictor of:

  • Autoimmune gastritis and pernicious anemia (90% of patients with these conditions have APCA)
  • Chronic Helicobacter pylori gastritis
  • Type 1 Diabetes
  • Thyroid disorders (30% of Hashimoto’s thyroiditis patients test positive)
  • Gastric cancer
  • Peptic ulcer disease
  • Myasthenia gravis
  • Addison’s disease
  • Iron deficiency anemia
  • Vitiligo
  • Alopecia areata

Clinical Importance

  • APCA is highly specific for autoimmune gastritis and pernicious anemia, making it a valuable early marker for these conditions.
  • If APCA is positive, additional tests for intrinsic factor antibodies, vitamin B12 levels, and gastric function may be required to confirm the diagnosis.

This test is essential for detecting autoimmune-related gastric and hematological disorders before clinical symptoms become severe