<<Disclaimer: Verify this information before applying it to your situation.>> I asked how tTG worked and why it would be useful for a diagnosed celiac. I got many responses (about half of them asking me to summarize). The main thought on why they'd be useful to a diagnosed celiac was "to test for diet compliance" which is the same use for which the traditional battery of tests is used. I had been hoping for a test capable of diagnosing the disease while on a gluten-free diet. I know there is one of these in testing (I believe it's called a "rectal challenge" which probably tells you more than you want to know about it). I got a very concise reply from Tom Ryan, Technical Service Specialist at INOVA Diagnostics, Inc. who make the test. He answered with just about everything you could want to know about the test, so I will quote his message here: "Celiac disease and dermatitis herpetiformis, more specifically termed gluten sensitive enteropathy are essentially the same disease but with different clinical presentations. It is an inability of the body to process the protein gliadin properly. Gliadin is a fraction of the gluten protein found in wheat and some other cereal grains. The body produces IgA and IgG antibodies to this protein. "This results in an inability to digest and absorb it properly and gives rise to the production of antibodies to the sheaf of fibers that surround the smooth muscle layer of the small intestine. This is called the endomysium and it is the presence of these IgA type antibodies that is being tested for with the endomysial antibody test. The IgA antibodies are very specific for celiac disease. IgA type endomysial antibodies are not found in any other condition. This test is very subjective, however. It involves applying some of the patient's serum to a section of tissue fixed onto a glass slide, treating it with various solutions, and viewing it under a fluorescent micrscope. If the endomysium surrounding the muscle fibers shows a green, glowing fluorescence, the test is positive. This involves a great deal of expertise and judgement viewing the slide and is subject to interpretation. Tissue transglutaminase has been identified as the protein that is actually being targeted in the endomysium and the tTG test has been developed to measure antibodies to this protein directly rather than looking for its visual effect on the endomysium so it's easier, faster and less subjective than the endomysial test. "A very small percentage of celiac patients are IgA deficient, not all of them. Only about 2-4% of them show this deficiency. Still, - - this is significantly higher than the general population where only about one half of a percent of the people are IgA deficient. It is significant enough to look for an additional tool to diagnose this disease. It has been found that those who are IgA deficient are usually IgG positive and that is the reason for testing for IgG. To catch the rare patient who is IgA deficient. "None of these tests, or any others, can report accurate results if the patient has been following a GF diet because the challenge by gluten in the diet is necessary to trigger the body to produce these antibodies or to cause a change in the jejunum that would be observable by endoscopy or detectable by biopsy." My thanks to Tom Ryan for the detailed answer, and to the many of you who shared what they knew about the test, too. -- Linda Blanchard Midland, Texas, USA http://www.nowheat.com celiac safe foods database, primer and more