Transglutaminase IgA

Transglutaminase IgA (anti-tTG IgA) is a blood test measuring IgA antibodies against tissue transglutaminase and is the primary test for detecting coeliac disease. It is reliable only if you regularly eat gluten and do not have immunoglobulin A deficiency, so total IgA is measured alongside it.

Who the test is for

• people with persistent diarrhoea, bloating, abdominal pain or symptoms resembling irritable bowel syndrome;
• people with unexplained weight loss and prolonged fatigue, and children with poor growth and development;
• people with anaemia due to iron, vitamin B12 or folic acid deficiency without a clear cause;
• people with severe or recurrent mouth ulcers or an itchy, blistering rash (dermatitis herpetiformis);
• people with persistently elevated liver enzymes of unknown cause or osteoporosis;
• people with type 1 diabetes, autoimmune thyroid disease, Down or Turner syndrome;
• people whose parent, sibling or child has coeliac disease.

What coeliac disease is and what the test indicates

Coeliac disease is a chronic autoimmune disease. In genetically susceptible people, gluten, a protein in wheat, rye and barley, triggers an immune reaction that damages the small intestinal lining, reducing nutrient absorption. It affects approximately one person in a hundred, can occur at any age, and many people remain unaware of it for years.

While a person with coeliac disease eats gluten, the body produces antibodies against tissue transglutaminase. High levels strongly suggest coeliac disease. Levels gradually fall on a gluten-free diet, so the test is also used to monitor dietary adherence after diagnosis. Gluten’s role is described in more detail in Coeliac disease – the role of gluten.

Preparation: do not eliminate gluten before testing

The test uses venous blood and does not require fasting. Most importantly, do not stop eating gluten before testing. British guidelines (NICE) advise eating gluten-containing food in more than one meal daily for at least six weeks before testing. If you already follow a gluten-free diet, the test may be falsely negative. Discuss reintroducing gluten or an alternative investigation pathway with your doctor.

Why total IgA is measured alongside transglutaminase IgA

Immunoglobulin A deficiency is more common in people with coeliac disease than in the general population. People lacking enough IgA cannot produce IgA antibodies, so transglutaminase IgA may be falsely negative despite disease. It is therefore measured alongside total IgA, and in deficiency a doctor uses IgG tests, such as transglutaminase IgG.

How results are interpreted

Results are expressed in units, with the positive cut-off depending on the method and printed on the report. A doctor interprets results alongside symptoms, total IgA and how much gluten you eat.

A negative result

If total IgA is normal and you regularly ate gluten, coeliac disease is unlikely. False negatives are possible with insufficient gluten intake, IgA deficiency or medicines that suppress the immune response. If symptoms persist, a doctor may recommend further investigation.

A positive result

A positive result suggests coeliac disease but is not a final diagnosis. Low positive values are less reliable and can also occur in other diseases. A gastroenterologist confirms the diagnosis. Adults generally undergo gastroscopy with samples of the duodenal lining. Under European paediatric gastroenterology guidelines (ESPGHAN, 2020.), children may be diagnosed without biopsy if transglutaminase IgA is at least ten times the upper limit and endomysial antibodies are confirmed in a second blood sample. Continue eating gluten until investigations are complete.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed on the Contact page). Prices for all tests and panels are available in the service price list. To have total IgA and transglutaminase IgG tested at the same time, choose the Coeliac Disease Panel, which also includes faecal calprotectin as an intestinal inflammation marker, so a stool sample is submitted alongside blood.

Frequently asked questions

Do I need to eat gluten before a coeliac disease test?

Yes. Antibodies are produced only while you eat gluten, so testing after starting a gluten-free diet could be normal despite coeliac disease. Do not change your diet until investigations are complete.

What does high transglutaminase mean?

High transglutaminase IgA most often indicates coeliac disease, particularly at high levels. However, a gastroenterologist diagnoses it based on additional tests; the blood test alone is not a reason to immediately eliminate gluten.

Is a coeliac disease test the same as a gluten intolerance test?

No. Transglutaminase IgA tests for coeliac disease. A genetic test shows whether you have the genes required for coeliac disease: if absent, coeliac disease is practically excluded, but their presence does not mean disease, because many healthy people also have them. Food IgG antibody tests are not used to diagnose coeliac disease, allergy or intolerance.

Can the test be negative even if I have coeliac disease?

Yes, most often when gluten intake was insufficient or total IgA is deficient. Testing is therefore performed while eating a usual gluten-containing diet and alongside total IgA.