CELIAC DISEASE TESTING

People have lots of questions about how to get tested, if they should get tested, what if the tests come up negative yet they feel the test is wrong.

The full celiac panel from Celiac.com is:

• tTG IgA and tTG IgG
• DGP IgA and DGP IgG
• EMA IgA
• Total serum IgA
• AGA IgA and AGA IgG (older and less reliable tests)
• Make sure you are eating gluten until testing is done,
• Many celiacs are low in some nutrients such as calcium, iron, ferritin, potassium, zinc, A, D, B12, and copper.
• Bone density can be an issue and should be checked.
• Thyroiditis as symptoms similar to celiac disease, as well as being associated with celiac disease. Getting checked for hypothyroidism is often helpful.

Here is an interesting article from Dr. Sheila Crowe, a professor in gastroenterology and hematology at the University of Virginia, to answer those questions in detail.

The ABCs (and TTGs) of Celiac Disease Testing

First, by definition, a diagnosis of celiac disease requires abnormal microscopic findings in small intestinal biopsy specimens. One exception to this rule occurs when a patient has a skin condition known as dermatitis herpetiformis, in which case a characteristically abnormal skin biopsy result can substitute for checking intestinal biopsies.

Since getting an intestinal biopsy is not necessarily the first test anyone wants to undergo, it is fortunate that several blood tests are helpful during the initial steps of diagnosing celiac disease. These blood tests measure antibodies – usually IgA or IgG – that are made by immune cells to two main proteins.

One protein is an enzyme called tissue transglutaminase, or TTG, that is found in many cells of our body. TTG is released from the damaged intestine during active celiac disease, and antibodies to TTG are found to be elevated in the blood of most patients with untreated celiac disease.

The other protein to which the body’s immune system responds to abnormally in someone with active celiac disease (and occasionally in some other disorders) is a group of proteins found in gluten called gliadins.

TTG Tests for Celiac Disease

At present, the standard of care based on the National Institutes of Health consensus conference on celiac disease, which was held in June 2004 and recommended in the American Gastroenterological Association position statement on celiac disease published in Dec. 2006, is to check for celiac disease using the TTG IgA antibody test. This test will correctly predict the finding of celiac disease on intestinal biopsies roughly 90 to 95 percent of the time, although some recent studies suggest it is less sensitive than initially thought.

In some cases, the TTG IgA test result can be “false negative” – that is, results come back negative, even though celiac disease is actually present. False negatives can occur for various reasons, but the best known cause is a condition called IgA deficiency that people are born with. This immunodeficiency occurs in about one in 600 healthy individuals but is much more common in those with celiac disease.

To help prevent false negatives, most laboratories will measure the total IgA level at the same time as the TTG IgA level. If you are IgA deficient, then your total IgA level will be very low, and that means there’s a very good chance that the TTG IgA test will be inaccurate (falsely low or normal) because you can’t make IgA antibodies to TTG or gliadin. In this case, your doctor will need to proceed to intestinal biopsies to confirm the suspicion of celiac disease. Occasionally your doctor may order other blood tests, such as TTG IgG or DGP IgG, if they are available.

An earlier blood test that detected IgA antibodies to TTG called the antiendomysial antibody, or EMA, test is more expensive and time-consuming to perform than the current automated method of testing for TTG, so EMA testing is rarely done now. Another blood test that measures IgG antiobidies to TTG is rarely tested for in most laboratories.

Gliadin Tests for Celiac Disease

The first antibodies to gliadin that were used for celiac disease testing are called antigliadin, or AG, antibodies, which are available in both IgA and IgG forms. Most diagnostic laboratories run AG tests for both types of antibodies.

More recently, researchers found that the body makes IgA and IgG antibodies to a form of gliadin called deamidated gliadin peptide, or DGP. Some laboratories are starting to test for these antibodies, too. These new DGP tests seem to be more accurate than the older generation of AG tests.

In adults, AG antibody tests are no longer recommended, as they are not very likely to correctly predict the findings of intestinal biopsies, with both false negative and false positive results. AG tests are reported to be elevated in quite a few other conditions, including Crohn’s disease, small intestinal bacterial overgrowth, food intolerances (including gluten sensitivity without celiac disease) and irritable bowel syndrome. AG tests may even be elevated in healthy individuals.

The DGP antibodies seem to be more accurate than the AG tests, with fewer false positive results than the TTG IgA test. However, at this time, the DGP antibodies are not routinely available for clinical use.

Celiac Blood Tests in Young Children

In young children, the TTG test is less sensitive – that is, it is less likely to be positive when celiac disease is actually present — than in adults. Therefore, both AG and TTG antibodies are checked in young children.

Saliva and Stool Tests for Celiac Disease

Another important point is that all of the information we have discussed above relates to blood antibody tests only. While antibody tests have been developed using saliva and stool, these tests are not sufficiently scientifically validated to be acceptable to the general scientific and medical community at this time. TTG tests are available to consumers for purchase in Canada but they are not approved for use in the United States.