Is an IgA (Immunoglobulin A) result from a celiac panel the same as a tissue transglutaminase (TTG) antibodies test result?

IgA vs TTG in Celiac Disease Testing

No, an IgA result alone from a celiac panel is not the same as a TTG test result. The primary test for celiac disease is specifically IgA tissue transglutaminase antibody (tTG-IgA), not just a total IgA measurement 1.

Understanding the Difference

• Total IgA: Measures the overall level of Immunoglobulin A in the blood

  • Used to identify IgA deficiency (occurs in 2-3% of celiac patients)
  • Not specific for celiac disease itself
  • Often ordered alongside tTG-IgA to rule out false negatives due to IgA deficiency

• tTG-IgA: Measures antibodies specifically targeting tissue transglutaminase

  • The primary serological test for celiac disease
  • High sensitivity (97.7% in children) 1
  • Moderate specificity (70.2% in children) 1

Clinical Implications

When you order a "celiac panel" but only receive an IgA result, several possibilities exist:

1. Only total IgA was measured (incomplete testing)
2. The lab may have used terminology that doesn't clearly distinguish between total IgA and tTG-IgA
3. The lab may have a reflex testing protocol where they first check total IgA before proceeding

What to do next:

• Contact the laboratory to clarify exactly what test was performed
• Request the complete celiac panel including tTG-IgA if not already done
• Consider IgG-based testing if the patient has IgA deficiency (total IgA < 0.06 g/L)

Best Practice for Celiac Testing

The American College of Gastroenterology recommends:

1. Primary test: tTG-IgA (not just total IgA) 1
2. Additional testing: Total IgA to rule out IgA deficiency
3. For IgA deficient patients: IgG-tTG or IgG deaminated gliadin peptides (DGP) 1

Important Considerations

• Testing should be performed while the patient is on a gluten-containing diet 1
• Some laboratories use tTG-IgA levels to predict IgA deficiency (values <0.10 μ/mL may indicate need for total IgA measurement) 2
• Simultaneous detection of both IgA and IgG antibodies against tissue transglutaminase (IgA/IgG anti-TG2) has shown excellent sensitivity (96%) and specificity (99.5%) 3

Pitfalls to Avoid

• Don't assume total IgA alone is sufficient for celiac screening
• Don't interpret a normal total IgA as ruling out celiac disease
• Don't stop at IgA testing if clinical suspicion is high
• Don't forget that approximately 2-3% of celiac patients have IgA deficiency, which can lead to false-negative tTG-IgA results 1

If you've only received a total IgA result, you should specifically request tTG-IgA testing to properly evaluate for celiac disease.