Anti-tissue transglutaminase antibodies: what they are, what they tell you and when they’re tested

Anti-tissue transglutaminase (anti-tTG) antibodies are the first blood test for coeliac disease. In people with coeliac disease, gluten sets off an immune reaction against the gut, and the body makes these antibodies. The test looks for the IgA type, together with total IgA.

When they’re tested

Doctors order them when you have symptoms that suggest coeliac disease: diarrhoea or bloating that does not settle, weight loss, iron-deficiency anaemia with no clear cause, ongoing tiredness, frequent mouth ulcers, raised liver enzymes for no reason. They are also done in close relatives of someone with coeliac disease and in people with other autoimmune conditions, such as type 1 diabetes or thyroiditis.

In Italy, the Ministry of Health protocol sets anti-tTG IgA together with total IgA as the first test, in both children and adults. The tests for the diagnosis are provided by the national health service.

In adults they are not done across the board in people who feel well and have no risk factors. That is why Rosa does not test them. Instead it looks at the marks coeliac disease often leaves in the blood: low ferritin and haemoglobin, small red cells (MCV) and raised liver enzymes.

What they tell you, and what they do not

If they are positive, coeliac disease is likely, but the test alone is not enough for a diagnosis. In Italy, in adults, the diagnosis is usually confirmed with endomysial antibodies (EMA) and a gastroscopy with a gut biopsy.

If they are negative and total IgA is normal, coeliac disease is unlikely, as long as you are eating gluten. If you have already cut gluten out, the test can come back falsely negative.

If total IgA is very low, the IgA test does not work. Your doctor then asks for the same antibodies in their IgG form.

That is why they are read together with other tests:

• Immunoglobulins: Total IgA shows whether the test can be trusted
• Ferritin: Low when the gut absorbs little iron
• Haemoglobin: Anaemia is often the first sign
• Liver enzymes (ALT and AST): Sometimes raised for no other reason

Normal anti-tTG levels

There is no single value for everyone. Each lab uses a kit with its own units and its own limit, printed on the report: below it is negative, above it positive. That is why numbers from two labs cannot be compared.

How many times the value exceeds the limit matters. A value just above needs confirming. A very high value makes coeliac disease very likely: in children, if it is at least ten times the limit and a second test (EMA) confirms it, a specialist can make the diagnosis without a biopsy. In adults the Italian protocol still asks for a biopsy. The latest European guidelines allow it to be skipped only in some selected adults with very high values, followed at an expert centre: the specialist decides.

Before the blood draw you should eat gluten as usual. You do not need to fast.

If your anti-tTG is high or negative

• High anti-tTG: Coeliac disease is likely. Do not cut out gluten: the other diagnostic tests come first.
• Negative anti-tTG: With normal total IgA and a diet that includes gluten, coeliac disease is unlikely.

What to do if they are positive

These are the usual steps:

• Keep eating gluten until the diagnosis is settled. Cutting it out early can make the next tests negative.
• Your doctor refers you to a gastroenterologist, or a coeliac centre, for EMA and a gastroscopy with biopsy.
• If the diagnosis is confirmed, the treatment is a lifelong gluten-free diet, with help from a dietitian. In Italy a certified diagnosis gives you an allowance for gluten-free food.
• On the diet, the antibodies fall. The first check is usually six months to a year after diagnosis, then once a year.

Do not start a gluten-free diet before you have been tested: if you later want a diagnosis, you will need to eat gluten again for weeks.

What can skew the result

A few things change the result without changing the diagnosis.

• A diet with little or no gluten: The antibodies fall and the test can come back negative even in people with coeliac disease.
• Low total IgA: IgA deficiency is more common in people with coeliac disease and makes the IgA test falsely negative.
• Medicines that dampen the immune system: Steroids and immunosuppressants can lower the antibodies. Do not stop them on your own: talk to your doctor.
• Other conditions: A value just above the limit is sometimes seen in other autoimmune or liver conditions. That is why it is confirmed with other tests.

When to worry

Talk to your doctor if:

• Your anti-tTG is positive: do not cut out gluten, and ask how to proceed.
• You have had diarrhoea, bloating or tummy pain for weeks, or you are losing weight without trying.
• You have iron-deficiency anaemia that has no explanation or keeps coming back despite treatment.
• A close relative has coeliac disease, or you have type 1 diabetes or autoimmune thyroiditis.
• You have severe tummy pain that will not go away, constant vomiting, or black stools or stools with a lot of blood: call 112 or go to the emergency department.

Frequently asked questions

What are normal anti-tTG levels? It depends on the lab’s kit. Your report prints a limit: below it is negative, above it positive. The further above the limit, the more likely coeliac disease is.

Positive anti-tTG: do I have coeliac disease? It is likely, but not certain. In adults the diagnosis is usually confirmed with a gastroscopy and a gut biopsy, often after endomysial antibodies. Until then, keep eating gluten.

Can I take the test if I already eat gluten-free? The result could be falsely negative. Talk to your doctor: they will tell you whether and how to bring gluten back before the blood draw.

Why is total IgA measured as well? The most common test looks for IgA-type antibodies. If your total IgA is very low, the test comes back negative even if you have coeliac disease. In that case your doctor uses IgG tests.

Gluten upsets me but my tests are negative: what does it mean? Coeliac disease is unlikely, if you were eating gluten. Your symptoms may have other causes, such as non-coeliac gluten sensitivity or irritable bowel. Better to work it out with your doctor before changing your diet.

Does Rosa test anti-tTG antibodies? No. Rosa measures ferritin, haemoglobin, MCV and liver enzymes, which often show the first signs of coeliac disease. If your doctor wants anti-tTG, they order it separately.

Sources

• Italian Ministry of Health, protocol for the diagnosis and follow-up of coeliac disease, Gazzetta Ufficiale 191/2015, as summarised by the Italian Coeliac Association. Ministero della Salute, GU 191/2015
• Al-Toma and colleagues, European Society for the Study of Coeliac Disease (ESsCD) guideline for coeliac disease and other gluten-related disorders. United European Gastroenterology Journal, 2019. PMID 31210940
• Al-Toma and colleagues, European Society for the Study of Coeliac Disease 2025 updated guidelines on the diagnosis and management of coeliac disease in adults. Part 1: diagnostic approach. United European Gastroenterology Journal, 2025. PMID 40999951
• Husby and colleagues, ESPGHAN guidelines for diagnosing coeliac disease 2020. Journal of Pediatric Gastroenterology and Nutrition, 2020. PMID 31568151