Tissue Transglutaminase (tTG) IgA
A blood test for antibodies to tissue transglutaminase, a gut enzyme. It is the main blood test used when celiac disease is suspected.
AI-verified against cited sources. Awaiting expert reviewAlso called tTG IgA, tTG-IgA, TTG IgALOINC 31017-7
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What it is
Celiac disease is an autoimmune condition in which eating gluten, a protein in wheat, barley and rye, harms the lining of the small intestine. In celiac disease the immune system makes antibodies against an enzyme called tissue transglutaminase (tTG). This test measures the IgA type of those antibodies in your blood. It works best if you make enough IgA, so labs often check total IgA as well. Labs use different test kits, so the cutoff on your own report matters more than the number alone.
Why it matters
In people who make enough IgA, tTG IgA is the most sensitive and specific blood test for celiac disease. A positive result usually leads to a biopsy of the small intestine, which is how celiac disease is confirmed in most adults. In some children, a very high result can be enough without a biopsy. After someone starts a gluten-free diet, the level usually falls, so the test is also used to see how the diet is working. It only works if you are still eating gluten when the blood is drawn.
If it’s high
A result above your lab's cutoff means tTG IgA antibodies were found. This fits with celiac disease, and also with dermatitis herpetiformis, a gluten-related skin rash. It is a strong clue but not a diagnosis, because clinicians usually confirm it with a biopsy. A weak positive is less certain than a high result, and results also depend on which kit your lab uses.
Common causes
- A weak positive that does not turn out to be celiac disease, since no antibody test is perfect
- In someone already treated for celiac disease, levels that stay high can mean some gluten is still getting in
- Dermatitis herpetiformis, an itchy blistering rash linked to gluten
- Celiac disease, the most common reason for a clearly positive result
What can help
- Keep eating gluten until all testing is finished, unless your clinician tells you otherwise
- Ask whether total IgA should be checked too
- Ask whether a biopsy, or other celiac blood tests such as endomysial antibodies, are the next step
- If you already follow a gluten-free diet, ask a dietitian who knows celiac disease about hidden sources of gluten
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 0–10 U/mL. Source: Labcorp, Mayo Clinic Laboratories.
- Adults (this one applies)0–10 U/mL
Sources: Labcorp, Mayo Clinic Laboratories
If this applies to you
tTG IgA means a little more for some people. Open the one that fits you.
Celiac disease or IBD
ACG uses tTG-IgA as the main first blood test for celiac disease, measured on a regular diet that includes gluten. Once celiac disease is confirmed, it is repeated to see whether the antibody turns negative on a gluten-free diet.
Low iron or anemia
In the UK, celiac disease is the most common cause of poor iron absorption, BSG notes. It recommends routine celiac testing in iron deficiency anemia, where celiac disease is found in 3% to 5% of cases. AGA suggests celiac blood tests first in adults with iron deficiency anemia and no symptoms when celiac disease is plausible.
What can affect your result
- Gluten intake: antibodies fall on a gluten-free diet, so the test needs to be done while you are eating gluten
- Total IgA: low or missing IgA can make tTG IgA falsely low
- Test kit: units and cutoffs differ between labs, for example negative below 4.0 U/mL at Mayo, below 7.0 at Labcorp, below 15.0 at Quest, and a different scale (FLU) at ARUP
- Age: for children under 2, other antibody tests such as DGP are often added
- A gluten-free diet before the test lowers the antibodies and can give a negative result. Antibody tests for celiac disease should be done while you are eating gluten (MedlinePlus, ARUP, Mayo).
- Low or missing IgA makes tTG IgA falsely low, so labs read it with total IgA, or add an IgG-based test (Mayo, ARUP).
- Kits differ in units and cutoffs (negative below 4.0 U/mL at Mayo, below 7.0 at Labcorp and below 15.0 at Quest; ARUP uses FLU), so only compare results from the same lab and kit.
- Samples with hemolysis, lipemia or bacterial contamination can be rejected by the lab (Labcorp).
After a gluten-free diet starts, antibody levels usually fall, but Mayo notes it can take up to 1 year for them to return to normal.
When to talk to a clinician
Talk with a clinician if you have ongoing diarrhea, bloating, belly pain, weight loss, low iron or anemia, an itchy blistering rash, or mouth sores. If you are tested for celiac disease, ask before you stop eating gluten, because a gluten-free diet can make the test look normal.
Questions you could ask
- How long should I keep eating gluten before testing?
- If my result is negative but I still have symptoms, which other celiac tests make sense?
- Should I have a biopsy or other tests to confirm this result?
- Should my total IgA be checked?
- Should close family members be tested?
Questions people ask
Do I need to keep eating gluten before the test?
Yes. Antibodies fall on a gluten-free diet, which can make the test look normal. MedlinePlus advises eating gluten for a few weeks before testing, and your clinician can tell you what fits your situation.
What does a weak positive result mean?
A weak or equivocal result, for example 4.0 to 10.0 U/mL at Mayo or 7.0 to 10.0 U/mL at Labcorp, is less certain than a high result. Your clinician may add another blood test, such as endomysial antibodies, or suggest a biopsy.
Why is my lab's cutoff different from another lab's?
Each lab uses its own test kit. Some report a negative result below 4 U/mL, others below 7 or 15 U/mL, and one reports in a different unit (FLU). Compare your result only with the range printed on your own report.
Show the science and sources
For clinicians and researchers
tTG IgA targets tissue transglutaminase (transglutaminase 2). ESPGHAN 2020 recommends measuring total serum IgA and IgA antibodies against transglutaminase 2 (TGA-IgA) as the best first-line combination, an IgG-based test only if total IgA is low or undetectable, and says that in children a TGA-IgA of 10 times the upper limit of normal or more, with positive endomysial antibodies in a second sample, can allow diagnosis without biopsy. The 2023 ACG guideline update describes serum antibodies such as tTG as very helpful for initial testing, intestinal biopsy as required in most patients, and a non-biopsy strategy as suggested for selected children. Mayo cites a multi-cohort study in which a tTG IgA of 10 times the upper limit of normal or more had a positive predictive value of 95% in adults. Kit performance varies: in a 2009 comparison of four tTG IgA kits and three deamidated gliadin peptide kits at the manufacturers' cutoffs, sensitivity ranged from 71.4% to 96.4% and specificity from 87.5% to 100%, and overall sensitivity was at or below 90%. Cutoffs: Mayo (ELISA, LOINC 46128-5) below 4.0 U/mL negative, 4.0 to 10.0 weak positive, above 10.0 positive; Labcorp (EliA, LOINC 31017-7) reference range 0.0 to 10.0 U/mL, with below 7.0 negative, 7.0 to 10.0 equivocal and above 10.0 positive; Quest (immunoassay) below 15.0 U/mL; ARUP (particle-based multianalyte technology, LOINC 46128-5) 0.00 to 4.99 FLU, with values of 50 FLU or more correlating better with biopsy findings and 5 to 10 FLU prompting added endomysial testing. Antibody levels fall after a gluten-free diet starts and can take up to a year to normalize (Mayo). Persistently elevated levels suggest ongoing gluten exposure or, rarely, refractory celiac disease. In dermatitis herpetiformis the antibody pattern can be more variable, so Mayo recommends endomysial antibody testing alongside tTG.
LOINC 31017-7 (primary), 46128-5, 35285-6, 35280-7. Specimen: serum.
Sources
- Tissue Transglutaminase Antibody, IgA, Serum (test TTGA), Mayo Clinic Laboratories
- Tissue Transglutaminase (tTG), IgA (test 164640), Labcorp
- Tissue Transglutaminase (tTG) Antibody (IgA) (test 8821), Quest Diagnostics
- Tissue Transglutaminase Antibody, IgA (test 3016860), ARUP Laboratories
- European Society Paediatric Gastroenterology, Hepatology and Nutrition Guidelines for Diagnosing Coeliac Disease 2020, Journal of Pediatric Gastroenterology and Nutrition (2020)
- American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease, American Journal of Gastroenterology (2023)
- Celiac Disease Screening, MedlinePlus (U.S. National Library of Medicine)
- Comparison of commercially available serologic kits for the detection of celiac disease, Journal of Clinical Gastroenterology (2009)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.