Transglutaminase IgG

Transglutaminase IgG is a blood test for coeliac disease intended primarily for people with immunoglobulin A (IgA) deficiency. In these people, the standard test, transglutaminase IgA, may be false-negative, so the IgG test helps prevent coeliac disease being missed. It is reliable only if you regularly eat gluten.

Who is this test for

• people with known total IgA deficiency who have symptoms resembling coeliac disease;
• when coeliac testing has also identified low total IgA;
• for prolonged diarrhoea, bloating, weight loss, fatigue or anaemia, when the doctor is investigating coeliac disease and the IgA level is unknown;
• children with delayed growth and development, as assessed by a paediatrician;
• family members of people with the disease and people with type 1 diabetes or autoimmune thyroid disease, if they have IgA deficiency;
• people with coeliac disease and IgA deficiency, to monitor a gluten-free diet.

What the test reveals

Coeliac disease is an autoimmune disease in which gluten, a protein found in wheat, rye and barley, damages the lining of the small intestine. While a person with coeliac disease eats gluten, the body produces antibodies against the enzyme tissue transglutaminase. IgA-class antibodies are most often measured, but people with insufficient IgA cannot produce them.

IgA deficiency is more common in people with coeliac disease than in other people. IgG-class antibodies are then measured, and this test shows whether they are present. In people with normal IgA, transglutaminase IgG is less reliable than transglutaminase IgA, so it does not replace it.

The test and preparation

The sample is blood from a vein, and collection takes a few minutes. You do not need to fast. Most importantly, do not remove gluten before the test: the British NICE guidelines advise eating gluten-containing food in more than one meal a day for at least six weeks before testing. If you have already switched to a gluten-free diet, discuss the next steps with your doctor.

What your results mean

• A negative result with IgA deficiency and regular gluten intake makes coeliac disease unlikely. If symptoms persist, the doctor may suggest further investigations.
• A positive result suggests coeliac disease but is not a final diagnosis. The diagnosis is confirmed by a gastroenterologist, usually in adults through gastroscopy with samples of the duodenal lining. Continue eating gluten until the investigations are complete.
• Positive IgG with normal total IgA and negative transglutaminase IgA is less reliable and requires a doctor’s assessment.

The result is expressed in units, and the positive-result threshold depends on the method and is printed on the report. The doctor interprets the report alongside symptoms and total IgA.

How to arrange testing

You can come for blood collection without an appointment or referral at one of our branches throughout Croatia (listed on the Contactpage). Prices for all tests and panels are listed in the price list. Total IgA, transglutaminase IgA and transglutaminase IgG from one blood collection are combined in the Coeliac disease panel, which also includes faecal calprotectin as an indicator of bowel inflammation.

Frequently asked questions

Why is an IgG test performed if an IgA test exists?

Because of IgA deficiency. People with insufficient IgA may have a false-negative IgA test despite having the disease, while the IgG test then provides more reliable information.

How do I know whether I have IgA deficiency?

A total blood IgA test shows this, which is why it is performed alongside coeliac testing. IgA deficiency usually causes no symptoms, while some people with it have respiratory infections more often.

Do I need to eat gluten before testing?

Yes. Antibodies are produced only while you consume gluten in food, so a test after switching to a gluten-free diet may be normal despite coeliac disease being present. Do not change your diet until investigations are complete.

What if symptoms persist even on a gluten-free diet?

The most common cause is gluten consumed unintentionally in food. Less often, another disease is involved, and very rarely a form of coeliac disease that does not respond to diet. A gastroenterologist assesses the cause. Read more about diet in the article Gluten-free diet.