In short, not much. To answer this question, let’s assume that the question is referring to the IgG antigliadin antibody (IgG-AGA) and the IgA antigliadin antibody (IgA-AGA) tests.  These two anti-gliadin antibody tests were the first tests developed for celiac disease and appeared in the early 1980’s. They have similar accuracy to one another BUT they are only about 80% accurate overall. Given the wide availability of newer, more accurate tests, their use for diagnosis of celiac disease is not routinely needed or recommended. However, they may still be of use for testing in suspected gluten-related neurological disorders (Leffler, Schuppan. Am J Gastroenterol. 2010)(Dennis, Leffler. Real Life with Celiac Disease, AGA, 2010.)

The most common and modern blood tests used to diagnose celiac disease are:

• Tissue transglutaminase IgA antibody level (commonly referred to as "tTG")
• Deamidated Gliadin Peptide IgA/IgG antibody level (commonly referred to as DGP)

Here’s a short excerpt from Blood Tests in Celiac Disease on celiacnow.org.

“The most frequently used test is the tTG. It is accurate at detecting most people with celiac disease on a gluten-containing diet.¹  However, a minority of patients with celiac disease (~2%) do not produce any IgA antibodies. This is a condition called IgA deficiency and is generally asymptomatic but may be associated with increased risk of some infections. A person with celiac disease who has this condition will generally test negative with the tTG test regardless of celiac status. ^{2, 3}

This is why doctors often also test for serum total IgA. It’s also one of the reasons why the DGP test was invented. DGP can detect people with celiac people with IgA deficiency because it can test for two types of antibodies (IgA and IgG) in only one test. The person must be on a gluten-containing diet, however, just as the tTG test requires. There is also an IgG tTG test but it is less accurate than the IgG DGP test. Conversely, IgA tTG is more accurate than IgA DGP.

The Endomysial Antibody test (EMA) is an earlier version of the tTG test. It is not as widely available as tTG and is more expensive than tTG. For these reasons, it is seldom used these days.”

See https://www.bidmc.org/-/media/files/beth-israel-org/centers-and-departments/digestive-disease-center/celiac-center/celiacnow/blood_tests_in_cd_level_2.pdf for excerpt references.

Per Dr. Daniel Leffler, a celiac gastroenterologist at Beth Israel Deaconess Medical Center, it is important to note that while the modern celiac blood tests (tTG and DGP) are very accurate, they are not perfect. Some patients will have active celiac disease with a negative test or a false positive result (the test is positive but they either don’t have celiac disease or their celiac disease is well controlled).   A gastroenterologist skilled in celiac disease can help to sort through the sometimes challenging blood work results.

Reviewed October 14, 2022.