What is the difference between an IGA and TTG IGA test? Why is each important?

When testing for celiac disease, two of the most common tests run are the IGA and TTG IGA tests. They are related and have different functions in celiac testing. Celiac disease testing must be done while on a gluten containing diet.

The Immunoglobluin A or IGA test is a test of the functioning of the immune system. It detects antibodies or cells used to fight infection or disease in your body. More specifically, the IGA test looks for antibodies in the respiratory tract or digestive system.

The IGA test confirms the immune system is working properly. In celiac testing, the test needs to be in the normal or above normal range. Normal or above normal on the IGA test do not indicate celiac disease. It simply indicates the immune system has a basic level of function.

Next up, the Tissue Transgluaminase IGA or TTG IGA test is specific to celiac disease. The TTG IGA test is 93% sensitive and 98% specific to celiac disease. Which means, if you have a positive TTG IGA test, there is a very good chance celiac disease is to blame.

More specifically, the TTG IGA test is not 100% sensitive or specific and there are other potential causes for a positive test. Some possible causes for false positive TTG IGA include Type 1 Diabetes, autoimmune liver or thyroid disease, autoimmune arthritis, or heart failure.

The TTG IGA is not 100% specific or accurate. Accurate celiac diagnosis requires a biopsy. The only exception is a triple positive diagnosis.

The TTG IGA is one leg of the triple positive celiac diagnosis. If the TTG IGA is over 10x normal, then celiac is likely. To be clear, if normal is 4 or below, 10x normal would be 40 or above.

If the IGA test is below normal, the TTG IGA test is not valid. It means that other tests in the celiac panel must be run in order to obtain screening blood tests for celiac disease, like the TTG IGG test. But that is for another post.

Also, remember, this is not medical advice, please consult with a board certified gastroenterologist regarding your celiac disease test results.

Sensitivity and specificity TTG IGA study -> https://loom.ly/pFoR2hs

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