A 38-year-old woman with long-standing coeliac disease presents with IgA deficiency (serum IgA <0.05 g/L). She is still symptomatic on a strict gluten-free diet for 12 months. Which antibody test should be used for serological monitoring in IgA-deficient coeliac disease?

• A IgA anti-tissue transglutaminase (IgA anti-tTG)
• B IgA anti-endomysial antibody
• C Total serum IgA repeat testing
• D IgG anti-deamidated gliadin peptide (IgG anti-DGP) ✓

Explanation

In IgA-deficient patients, IgA-based serological tests (IgA anti-tTG, IgA anti-EMA) will produce false-negative results. The alternative is IgG-based testing: IgG anti-deamidated gliadin peptide (IgG anti-DGP) or IgG anti-tissue transglutaminase (IgG anti-tTG). IgG anti-DGP has the best sensitivity (approximately 80–90%) in IgA-deficient coeliac disease. This is the recommended approach per ACG 2023 coeliac disease guidelines when total IgA is low.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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