A 24-year-old woman has chronic diarrhea and iron deficiency anemia suggestive of coeliac disease. Tissue transglutaminase IgA antibody is negative on two occasions. Total serum IgA level is 0.04 g/L (normal 0.8 to 4.0). Which test should be used next to evaluate for coeliac disease?
- A Deamidated gliadin peptide IgG or tTG-IgG antibody ✓
- B Repeat tTG-IgA after gluten challenge
- C Anti-endomysial IgA antibody
- D HLA-DQ2/DQ8 typing alone without serology
Correct answer: A. Deamidated gliadin peptide IgG or tTG-IgG antibody
Explanation
Selective IgA deficiency occurs in about 2 percent of coeliac patients and causes false-negative tTG-IgA and anti-endomysial IgA results. In such patients, IgG-based assays, either tTG-IgG or deamidated gliadin peptide IgG, retain diagnostic sensitivity. Repeating an IgA-based test will remain falsely negative, and HLA typing alone cannot confirm disease since DQ2 or DQ8 is present in roughly 30 percent of the general population. Duodenal biopsy remains confirmatory if IgG serology is positive.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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