Tissue Tranglutaminase Test - IgA

The tissue transglutaminase (tTG-IgA) test, also known as the tTG-IgA test, IgA anti-tissue transglutaminase test, or IgA anti-tTG test, is a blood test used to help detect coeliac disease. Coeliac disease is a long-term immune-mediated condition in which the body reacts to gluten, a protein found in wheat, rye, and barley, causing damage to the lining of the small intestine.

The test measures IgA antibodies against tissue transglutaminase, a protein that has been identified as an important target of the immune response in people with coeliac disease. Doctors may use the tTG-IgA test as the first step when coeliac disease is suspected because it is a useful screening test with high sensitivity and specificity. Previously undiagnosed cases of coeliac disease may also be detected through this test, even among people who do not experience clear symptoms.

A positive result may suggest coeliac disease and indicate the need for additional tests, such as an endomysial antibody (EMA) test or biopsy of the small intestine, to confirm the diagnosis. The primary focus of this test is the small intestine, which can become damaged in coeliac disease, and the immune system, which produces the antibodies measured by the test.

A doctor may advise a tTG-IgA test if a person has symptoms that may be linked to coeliac disease, such as:

• Frequent diarrhoea or loose stools
• Stomach pain or abdominal discomfort
• Bloating or excessive gas in the stomach
• Nausea or vomiting
• Constipation
• Unexplained weight loss
• Feeling unusually tired or lacking energy
• Bone or joint pain
• Itchy skin rash with blisters
• Mouth ulcers or dry mouth

Some people may also require this test because they have a higher chance of developing coeliac disease. These include people with:

• Immediate family members with coeliac disease
• Type 1 diabetes
• Autoimmune thyroid disease
• Autoimmune liver disease
• IgA deficiency
• Down syndrome
• Turner syndrome

The tTG-IgA test is not usually performed routinely for everyone. Doctors generally recommend this test when symptoms suggest coeliac disease, when a person belongs to a high-risk group, or when monitoring response to a gluten-free diet. The frequency of testing depends on the individual's symptoms, diagnosis, and treatment plan.

A tissue transglutaminase (tTG-IgA) test is primarily used to help identify coeliac disease and assess the immune response associated with the condition, as follows:

• Coeliac disease: An autoimmune condition in which eating gluten triggers an immune response that damages the lining of the small intestine. Elevated tTG-IgA antibody levels are strongly associated with coeliac disease.
• Undiagnosed or silent coeliac disease: The test may help detect coeliac disease in people who have mild symptoms or no obvious symptoms but still have intestinal damage caused by gluten.
• Active coeliac disease: Higher levels of tTG-IgA coeliac disease antibodies often correlate with active disease and ongoing immune response to gluten.
• Poor response to a gluten-free diet: In people diagnosed with coeliac disease, persistently elevated tTG-IgA levels may suggest continued gluten exposure or incomplete response to treatment.

What to Expect Before the Tissue Tranglutaminase IgA Test

No fasting is required for a standalone Tissue Tranglutaminase IgA test. You can eat and drink normally. However, if it is part of a broader package that includes fasting tests, your doctor may advise fasting for 8-12 hours. Avoid strenuous exercise for 24 hours before the test, as intense physical activity can temporarily raise Tissue Tranglutaminase IgA levels and affect interpretation. Always inform your doctor about any ongoing medications.

What to Expect During the Blood Collection

A phlebotomist cleans the skin with an antiseptic, then places an elastic band around your upper arm to make the veins easier to access. A small needle is inserted into the vein; you may feel a brief pinch. Blood is collected into a labelled tube in under a minute.

What to Expect After the Tissue Tranglutaminase IgA Test

A small cotton swab and bandage are placed over the site to stop any minor bleeding. You can return to normal activities immediately. Minor bruising is normal and disappears quickly. If dizzy, sit and rest for a few minutes.

This test measures one important antibody parameter:

• Tissue transglutaminase (tTG-IgA) antibodies: It measures the level of IgA antibodies against tissue transglutaminase, a protein targeted by the immune system in individuals with coeliac disease.

The tTG-IgA results are measured in arbitrary units per millilitre (AU/mL), a laboratory-specific unit used to report antibody levels. The tissue transglutaminase IgA normal range is a negative result, and values are given in the following table:

The tTG-IgA test result is interpreted by comparing the antibody level with the laboratory reference range as given in the table below:

The tTG-IgA blood test is a simple and safe blood test. However, like most blood tests, it has minor risks and some limitations.

Possible Risks of the Test

Some people may experience mild discomfort or notice a small bruise at the blood sample collection site. These effects are usually temporary and settle within a short time.

Limitations of the Tissue Transglutaminase (tTG-IgA) Test

• The test may be less sensitive in children younger than 2 years of age.
• Although the tTG-IgA test has high accuracy, a positive result alone may not be enough to confirm coeliac disease, and additional tests may be needed.
• The accuracy of the test may be reduced in people with IgA deficiency, and they may require additional tests, such as tTG-IgG.
• False-negative or false-positive results can occasionally occur due to factors such as immunosuppression, infections, autoimmune disorders, or borderline antibody levels.

Doctors may advise the following tests along with the tissue transglutaminase (tTG-IgA) test to help diagnose or confirm coeliac disease:

• Total IgA test
• Tissue transglutaminase (tTG-IgG) test
• Endomysial antibody (EMA) test
• Deamidated gliadin peptide (DGP) antibody test
• Coeliac disease antibody panel
• Upper GI endoscopy
• Small intestinal (duodenal) biopsy
• HLA-DQ2 and HLA-DQ8 genetic tests