Tissue transglutaminase antibodies (tTG-IgA)
Antibodies against tissue transglutaminase, the most common blood test for suspected celiac disease
Also known as
Definition
In celiac disease, the immune system reacts to gluten from wheat, barley and rye and produces, among others, antibodies against the body's own enzyme tissue transglutaminase (tTG). The tTG-IgA test measures these IgA-class antibodies in the blood and is the most commonly used screening test for celiac disease. Total IgA is usually measured as well, because IgA deficiency can affect the result. The test alone does not make a diagnosis.
| Parameter | Value |
|---|---|
| Unit | U/ml or other assay-specific units |
| Reference Range | No single numeric range: the result is usually reported as negative, weakly positive or positive relative to a cut-off of the specific test. Cut-offs and units differ between labs and assays; the range on your own report is what counts. Discuss your result with your doctor. |
Agree on your personal target range with your doctor.
↓ What a low value means
A negative result speaks against celiac disease, but is only meaningful if you have been eating gluten regularly in the weeks before the test. IgA deficiency can also lead to a normal tTG-IgA value; in that case IgG-based tests come into question. If symptoms persist, your doctor may arrange further assessment despite a negative result.
↑ What a high value means
A positive result may be related to celiac disease but does not confirm it on its own. In adults, it is usually followed by a tissue sample from the small intestine taken during an upper endoscopy; with weakly positive values, endomysial antibodies (EMA) are often tested as well. Switching to a gluten-free diet before the diagnosis is confirmed is not recommended, as this can distort later tests. In known celiac disease, the value is also used for monitoring. Your doctor interprets the result.
When to test
The test is considered, among other situations, with persistent unexplained digestive symptoms, prolonged fatigue, unintended weight loss, unexplained iron, vitamin B12 or folate deficiency, type 1 diabetes or autoimmune thyroid disease, and in first-degree relatives of people with celiac disease. According to NICE, gluten should be eaten in more than one meal every day for at least six weeks before testing; clarify preparation with your doctor.
Frequently asked questions
Should I eat gluten-free before the test? +
This is not recommended. The test is only meaningful while you are eating gluten. Cutting out gluten beforehand risks a false negative result. Talk to your doctor about how to prepare in your case.
Does a positive test mean I definitely have celiac disease? +
No. A positive result makes celiac disease more likely. In adults, it is usually confirmed or ruled out with a tissue sample from the small intestine, often supplemented by a further antibody test when values are weakly positive.
Why is total IgA often measured too? +
The tTG-IgA test detects IgA-class antibodies. If the body makes too little IgA overall, the value can be normal even though celiac disease is present. In IgA deficiency, labs therefore use IgG-based tests.
What is the test used for after a diagnosis? +
It helps with monitoring. On a gluten-free diet, antibody levels usually fall. If they stay high for a long time, this can be a reason for further tests, which your doctor decides on.
Tissue transglutaminase antibodies (tTG-IgA)
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.