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First, I sincerely apologize for not summarizing much sooner.

I had posted a request for information about the confusing tests for
celiac:
the tTg assay (done by U. of Md Celiac study, and others) and the HLA
typing which is a separate indicator for celiac genetic makeup.

I am not alone is not understanding the differences - I received 22
responses to my post:  11 responses were requests for a summary from
people who also  did not clearly understand the differences,  and 11
responses were from individuals who were unanimous in their explanation
that indeed the two types of testing are very different (and 5 of the
second group of 11 also requested a summary because they were not real
sure of the explanation they gave me--)
And thank you for the responses.

To summarize as best I can:

        -the tTg (tissue transglutaminase) assay is a series of 4 tests (IgA
autoantibodies, IgA + IgG gliadin autoantibodies, IgA endomysial
autoantibodies, and IgA reticulin antoantibodies) which, when all
evaluated together provide a 'probabability of celiac disease with high
accuracy.  When done in isolation, any of these
tests is less likely to be accurate in determining probability
of celiac disease.  Antibodies are only produced when a
gluten-intolerant person ingests gluten (which also presumably is
causing intestinal damage.)

        No gluten - no antibodies - negative tests ---
so -- if a celiac is fairly good at eliminating sources of gluten in the
diet, the tests won't be positive.  And if he is ingesting gluten
somewhere in am'ts large enough to produce antibodies (and cause
damage), the tTg assay will be positive (show increased probability of
celiac disease existing.)

        -the HLA typing (or 'genetic' test, GenotypR test) is used to search
for the gene sequences which are shared by those with celiac disease.
This test (NOT being done by U. of Md., I don't think--) does not
indicate whether the person currently HAS celiac disease - only whether
he is at risk for having the condition OR in some cases, may already be
gluten-intolerant.

It shows whether a person has the genetic capability of becoming celiac
without showing if a person HAS or does NOT yet have celiac.  If the
celiac associated alleles (gene sequences) are found, doing the tTg
assay (IF the person is NOT gluten-free) will show if that person is
producing ANTIBODIES because he has overt celiac disease.

RE: DH -- I asked the researcher @ U. of Md if these assumptions are
also true for DHers. She said that the tTg antibody assay was often NOT
POSITIVE in people with DH but THAT PERSON MUST STILL REMAIN GLUTEN-FREE
as damage to the small bowel mucosa is still occurring (with or without
GI symptoms.)

I have read on another WWW site that any "commercial" lab in the US
should be able to perform the HLA testing (GenotypR test for celiac.)
Due to time constraints, I have not found a  more local lab yet and
don't remember now where I read the statement about 'commercial labs'.
When (if) I find a lab in the East, I will post.  A positive HLA
(genetic) test in a g-f individual is probably not diagnostic of
gluten-intolerance, DH would then need to be confirmed by biopsy of a
lesion for accurate diagnosis.

Sorry for the length and I HOPE I got all this right -- if not, someone
please correct me?  :-)

Ruth Arcuri-Kovacs, VA

     (ADDENDUM: we have successfully set up a program in Winchester, VA to
      have blood drawn and sent via Winchester Med. Center laboratory to
      U. of MD for testing and it seems to be working well so far -- our
      projected date for 1st "planning" meeting of Celiac/DH Support Grp.
      of Northern Shenandoah Valley will be April 3 at the old "hospital."
      If all goes smoothly, will post details by end of the month.)