tTG-IgA Blood Test (Coeliac Screening)
A tTG-IgA blood test is used as part of the initial screening for coeliac disease. It looks for IgA antibodies that can develop when the immune system reacts to gluten. The test is usually arranged for people with digestive symptoms, nutritional deficiencies or when coeliac screening is clinically appropriate. A tTG-IgA result is never used alone to confirm or exclude a diagnosis.
What the tTG-IgA Test Measures
The test measures:
- Tissue transglutaminase (tTG) IgA antibodies, which may increase when the immune system reacts to gluten.
- Total IgA level, to ensure the body produces enough IgA for the test to be reliable.
If IgA levels are low, alternative tests may be used as advised by a clinician.
Why tTG-IgA Testing Is Used
A GP may arrange a tTG-IgA blood test to explore:
- Bloating or abdominal discomfort
- Changes in bowel habits
- Unexplained fatigue
- Low iron or B12 levels
- Unexplained weight changes
- Nutrient deficiencies
- Long-standing digestive disturbances
- Family history of coeliac disease
- Monitoring after dietary changes (under GP or specialist guidance)
For accurate results, you should be eating gluten regularly before the test unless advised otherwise.
Common Reasons to Have a tTG-IgA Test
- Persistent digestive symptoms
- Unexplained anaemia
- Abdominal discomfort after eating certain foods
- Ongoing tiredness without a clear cause
- Vitamin or mineral deficiencies
- Symptoms associated with gluten exposure
- Screening when clinically indicated
This test provides supportive information but cannot confirm or rule out coeliac disease on its own.
Understanding tTG-IgA Result Patterns
Raised tTG-IgA
A raised level may indicate an immune response to gluten. Further assessment is usually required, and interpretation always depends on symptoms, total IgA levels and clinical evaluation.
Normal tTG-IgA
A normal level does not always exclude gluten-related issues, particularly if symptoms persist or if IgA levels are low.
Low or Absent IgA
Some people naturally produce low IgA levels, which can make the tTG-IgA test less reliable. In these situations, other antibody tests may be used as advised by a clinician.
Results are never interpreted in isolation.
How the Test Is Performed
A small venous blood sample is taken from the arm.
You should continue eating gluten before the test unless a clinician advises otherwise.
Results usually return within 2 to 4 days.
When to Discuss tTG-IgA Results with a GP
Speak to a GP if:
- Your results fall outside the reference range
- You have ongoing digestive symptoms
- You have nutrient deficiencies
- You are unsure whether you should continue eating gluten
- You need guidance on next steps or further testing
- You are considering dietary changes
A GP can review symptoms, blood markers and nutritional patterns to decide whether additional assessment or specialist referral is appropriate.
Related Tests
tTG-IgA is often reviewed alongside:
For a wider overview of routine blood markers, you can visit our main Blood Tests section in the Knowledge Base.
If you would like to discuss digestive symptoms, nutrient deficiencies or blood test results, you can book an online GP appointment with AccessGP.
Last reviewed by Dr Zamiel Hussain, GMC registered GP
Updated: 8 December 2025