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John Dennis asked me to explain the implications of serological tests in
celiac disease. These are immunological tests. They are reflecting
whether there is an activation of the immune system in the patients. The
trigger for this immune response is the gliadin. The difference between a
celiac and non-celiac individual is that a non-celiac does not have
immune response to gliadin.

If a patient has active disease and he/she is on a non-restricted diet
the serological tests are positive, which means that he/she has
high concentration of antibodies in his/her serum.

We are performing three different tests:
   -anti-gliadin IgG antibody test
   -anti-gliadin IgA antibody test
   -anti-endomysium antibody test

The most sensitive and specific test is the anti-endomysium test, however
it can give false negative results in small children (<2 years of age) and
in patients with selective IgA deficiency. IgA deficiency occurs in one
out of 500-600 people. In IgA defificent patients only the anti-gliadin
IgG test will be positive, and additional absorptive studies are
necessary before the intestinal biopsy.

The combination of these three antibody measurements allows us to reach an
approximately 96% specificity and sensitivity. It means that we can miss
4% of patients if we rely on only the serological tests.

If somebody on a gluten-free diet these tests become negative by 6 month
of the gliadin-free diet. The decline of the initially high antibody
levels may suggest a good compliance. In the absence of the "gliadin
trigger" the immune system does not produce new antibodies, and generally
it takes 6 months to eliminate the "old antibodies". A  positive
test during a long-term diet indicates accidental gluten consumption.

The serological tests are useful in the diagnosis of celiac disease, and
helpful in the estimation of strictness of the diet.

If a celiac patients has some unusual symptom during the diet these
tests can help to estimate whether these symptoms are related to the
gliadin or we should look for some other reason. In Europe most of the
patients have serological test results at the time of diagnosis, on diet,
and during a rechallenge with gluten, which makes their management much
easier.

If you have any question concerning diagnostic tests in celiac disease me
and my colleagues will be happy to answer them. We established a
Celiac Center here at the University of Maryland to help children and
adults with celiac disease all over the U.S.

Karoly Horvath, M.D., Ph.D.