There are two different gluten tests that, which mean different things, but both carry the same “gliadin” name – this is confusing to everyone. The solution is to fully describe each test.
DGP gliadin confusion
With the introduction of a new gliadin test, the nomenclature celiac/ gluten tests has come even more confused. The problem is that the term gliadin test is now being used for both the new and the old tests. But these tests are very different from each other with different interpretation of the results.
DGP is a great new test
This new celiac test, the Deamidated Gliadin Peptide antibody test, is an excellent test. It was introduced to New Zealand in a limited way in 2006. Incrementally, it has become a routine test in the USA, Australia and now (since 4 August, 2009) by Medlab South, New Zealand: it is now part of their standard celiac panel (other laboratories have yet to adopt this test). Canterbury Health Laboratories offer this test since 2011.
The enthusiasm for the DGP assay is because it is extremely accurate for detecting the gut damage of celiac disease. It is more specific and more sensitive than the previous tTG/EMA tests. It has been developed as a specific celiac diagnostic tool by Inova Diagnostics. It is so good that this DGP test is likely to make endoscopy confirmation of celiac disease a redundant practice.
However, a problem has become apparent with the description of the DGP test. To best understand the confusion, you first need to know a little bit of the history of antibody testing for celiac and gluten problems.
The gluten antibody story
The old gliadin test. In the 1990s, the gliadin antibody test was developed. Although most celiacs had a positive IgG-gliadin antibody test, high levels of this antibody were found in about 10% of the normal population. Consequently, gliadin testing was considered non-specific” from the point of view of diagnosing celiac disease. Mistakenly, this led to IgG-gliadin being maligned as a useless and non-specific test .
Gluten sensitivity. The reality, however, is that an elevated IgG-gliadin antibody specifically means that the person is immunologically reacting to gluten. International research, including my own, has demonstrated that high gliadin anybody levels are frequently associated with clinical disease without the gut damage of celiac disease. This is now known as non-celiac gluten sensitivity, or the gluten syndrome.
Because of the poor predictive value of IgG-gliadin antibodies to detect celiac disease, this old gliadin test has been widely abandoned in the medical community – to the extent that most laboratories do not offer to do this test. But this is about to change.
EMA and tTG. Over the last 10 years, endomesial antibodies (EMA) and tissue transglutaminase (tTG) tests have been introduced with better diagnostic accuracy for detecting celiac disease. It has been the convention to confirm celiac disease by endoscopic biopsy for people who have tested positive to these EMA and/or tTG. To goal has been to develop a diagnostic test for celiac disease that will do away with the need for endoscopy.
DGP. This new deamidated gliadin peptide (DGP) antibody is the next big step along the journey. It is more sensitive and specific than EMA or tTG for the diagnosis of celiac disease. Unfortunately, its name is now being confused with the early old gliadin test.
Shortening names is universal, we call these nicknames. Whenever I am in Australia, I introduce myself as Rodney, but my friends call me Rod .
The same name strategy is being used for the DGP test. Instead of its full name, it has been shortened to the gliadin test – the identical name for the old gliadin test. But they test for very different things:
- The new DGP gliadin test accurately indicates the gut damage of celiac disease.
- The old IgG-gliadin antibody test indicates immunological reaction to gluten, and can help diagnose the gluten syndrome.
This is a bit like using the word bike to describe both pedal bicycles and motorbikes. They both have two wheels and a seat, but they have distinct properties and cannot be interchanged. But they are both useful. You have to know what sort of bike you are talking about.
Lab test report confusion
The labs who are now doing the DGP assay have added to this confusion. The following are statements made by laboratories reporting results. As you can read, their text fails to clarify the situation:
Gliadin IgA and IgG tests are now run using new generation Deamidated Gliadin Peptide IgA and IgG peptides as antigens. These assays show improved diagnostic accuracy (notably specificity) for celiac disease.
[This sounds to me as though they are still doing the old test but with new ingredients].
Antibody is to deamidated gliadin peptide are more specific for celiac disease than those detected by standard gliadin kits
[This suggest to me that the new gliadin in test is just a bit better than the old gliadin test. It gives no indication that it is a totally different test].
Other laboratories are simply using the terms Gliadin IgA and Gliadin IgG without any indication at all that the test is actually a Deamidated Gliadin test.
What does this all mean
There is already a lot of confusion. Good medical decisions require a full understanding of what tests are being done on what patients.
For over a decade the IgG-gliadin antibodies have been criticized as non-specific . Now suddenly you are being asked to accept these antibodies as accurate and reliable. This about-face will require a lot of education.
The old IgG-gliadin antibody test has been used by many people to diagnose the gluten syndrome. It is crucial that there is a clear distinction between the old and new test so that both the patients and the practitioners know what test has been done.
This is how to interpret what these gliadin antibodies mean:
- A positive old test (IgG-gliadin antibody) usually means gluten sensitivity.
- A positive new test (DGP-IgG and DGP-IgA) means celiac disease.
- A negative old test usually means that gluten is unlikely to be a problem.
- A negative new test means that celiac disease is unlikely at the time of the test, but it does not rule out gluten sensitivity.
As you can see, there is gliadin antibody confusion. The same name is being used for both tests, but they have different interpretations.
My suggestion is to have the medical laboratories always use the term DGP, and that more precise education material should accompany the results.
Dr Rodney Ford.
Author of The Gluten Syndrome