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Tissue Transglutaminase (tTG) IgG

A blood test for IgG antibodies to tissue transglutaminase, a gut enzyme. It is used for celiac disease testing mainly when IgA is low or missing.

AI-verified against cited sources. Awaiting expert reviewAlso called tTG IgG, tTG-IgG, TTG IgGLOINC 32998-7

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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 IgG type. Most people with celiac disease make the IgA type instead, so the IgG test is mainly used for people who have low or no IgA. Labs use different test kits, so the cutoff on your own report matters more than the number alone.

Why it matters

The usual first blood test for celiac disease is tTG IgA. That test can look falsely normal if your body makes little or no IgA, so a tTG IgG test is used instead. A positive tTG IgG is a clue but is less accurate than tTG IgA, so clinicians usually confirm it with a biopsy of the small intestine. 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 IgG antibodies were found. In someone with low or missing IgA, this fits with celiac disease. It is less specific than a tTG IgA result, so clinicians usually confirm it with a biopsy of the small intestine rather than relying on the blood test alone.

Common causes

  • A positive result that does not turn out to be celiac disease, because IgG tests are less accurate than IgA tests, especially in people with normal IgA
  • 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 in a person with low or missing IgA

What can help

  • Keep eating gluten until all testing is finished, unless your clinician tells you otherwise
  • Ask whether total IgA and a deamidated gliadin peptide (DGP) IgG test should be checked too
  • Ask whether a biopsy is 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.

  • Adults (this one applies)0–10 U/mL

    Source: Labcorp

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: this test is mainly useful when IgA is low or missing
  • Test kit: units and cutoffs differ between labs, for example negative below 6.0 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).
  • This IgG test is mainly used when total IgA is low or missing. It is less accurate than the IgA test in people who make normal IgA (ARUP, Mayo).
  • Kits differ in units and cutoffs (negative below 6.0 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

  • Why was the IgG test chosen for me instead of the IgA test?
  • Should I have a biopsy or other tests to confirm this result?
  • Should my total IgA and a DGP IgG test be checked?
  • Should close family members be tested?

Questions people ask

Why was I given an IgG test instead of the usual IgA test?

The IgA test can look falsely normal if your body makes little or no IgA. Labs and guidelines suggest an IgG-based test in that situation. Your clinician may check your total IgA to decide.

Does a positive tTG IgG mean I have celiac disease?

It is a clue, but not proof. ARUP and Mayo both note that IgG tests are less accurate than IgA tests, and a biopsy of the small intestine is usually needed to confirm celiac disease.

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.

Show the science and sources

For clinicians and researchers

tTG IgG is the IgG-isotype test for transglutaminase 2 antibodies. ESPGHAN 2020 recommends total IgA plus TGA-IgA as the first-line combination, and an IgG-based test only if total IgA is low or undetectable. ARUP recommends tTG IgG with deamidated gliadin peptide (DGP) IgG in IgA-deficient people, and states that a biopsy is required to establish the diagnosis because of the lower accuracy of IgG markers, especially in patients without IgA deficiency. Mayo states that tTG IgA is preferred over tTG IgG except in IgA deficiency, that a negative result lowers the likelihood of celiac disease, and that serology should not be solely relied upon to diagnose it. The 2023 ACG guideline update describes intestinal biopsy as required in most patients. Cutoffs: Mayo (ELISA, LOINC 56537-4) below 6.0 U/mL negative, 6.0 to 9.0 weak positive, above 9.0 positive; Labcorp (EliA, LOINC 32998-7) 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 56537-4) 0.00 to 4.99 FLU. Antibody levels fall after a gluten-free diet starts and can take up to a year to normalize (Mayo).

LOINC 32998-7 (primary), 56537-4, 53026-1. Specimen: serum.

Sources

  1. Tissue Transglutaminase Antibody, IgG, Serum (test TTGG), Mayo Clinic Laboratories
  2. Tissue Transglutaminase (tTG), IgG (test 164988), Labcorp
  3. Tissue Transglutaminase (tTG) Antibody (IgG) (test 11070), Quest Diagnostics
  4. Tissue Transglutaminase Antibody, IgG (test 0056009), ARUP Laboratories
  5. European Society Paediatric Gastroenterology, Hepatology and Nutrition Guidelines for Diagnosing Coeliac Disease 2020, Journal of Pediatric Gastroenterology and Nutrition (2020)
  6. American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease, American Journal of Gastroenterology (2023)
  7. Celiac Disease Screening, MedlinePlus (U.S. National Library of Medicine)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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