iga and iga deficiency
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The primary antibody class in the gut — and when it's missing, celiac blood tests go blind.
IgA (Immunoglobulin A) is the most abundant antibody class in mucosal tissues — the linings of the gut, lungs, and other surfaces exposed to the outside world. It's the immune system's first line of secreted defence at these barriers. The fact that celiac disease primarily affects the gut mucosa is why IgA-class antibodies are the most clinically relevant for both disease activity and diagnosis.
Why Celiac Tests Use IgA
The dominant autoantibody in celiac disease — anti-tTG — is produced as IgA because the immune reaction is happening in mucosal tissue. IgA-based tests (TTG IgA, EMA IgA) are more sensitive and specific for celiac than their IgG equivalents because they reflect where the disease actually lives.
IgA Deficiency
IgA deficiency is a condition where the body produces very little or no IgA. It is:
- The most common primary immunodeficiency (~1 in 500 in the general population)
- ~13× more common in celiac patients (~1 in 40)
- Usually asymptomatic (other immunoglobulin classes compensate)
The Diagnostic Problem
In a patient with IgA deficiency, all IgA-based celiac tests will return falsely negative — the anti-tTG IgA antibodies simply aren't being made. This is the most common cause of a false-negative celiac serology in clinical practice.
Guidelines therefore recommend simultaneously testing for IgA deficiency whenever ordering celiac serology. If IgA deficiency is confirmed, switch to IgG-based alternatives:
| IgA-based (first-line) | IgG-based (if IgA-deficient) |
|---|---|
| TTG IgA | TTG IgG (less accurate) |
| EMA IgA | EMA IgG |
| — | DGP IgG (deamidated gliadin peptide) |
DGP IgG is the preferred alternative in IgA deficiency — it has better performance characteristics than TTG IgG or EMA IgG in this setting.
IgA Deficiency and Disease Severity
The association between IgA deficiency and celiac disease likely reflects a shared underlying immune dysregulation — both conditions involve mucosal immune abnormalities. Patients with both conditions may have more severe or atypical presentations.
Related Concepts
autoantibodies-celiac | ttg-iga-test | diagnosis | glossary