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                          Celiac Blood Tests
                          ------------------
                        by Dr. Thomas Alexander
                        summarized by Jim Lyles
 
Dr. Thomas Alexander, a gastroenterologist out of Beaumont Hospital
and our group's physician advisor, spoke at our April meeting.  What
follows are some highlights of his talk.
 
Antibodies are proteins that the body makes to kill foreign invaders
(viruses, bacteria, etc.)  One of the first antibodies found that
could be used to diagnose CD was the antigliadin antibody.  Gliadin is
the part of gluten that seems to cause the problem for celiacs.  There
are two kinds of antigliadin antibodies:  IgA and IgG.  Tests for
these two antibodies will pick up about 90% of the patients with
untreated CD.  Once you start a GF diet, these antibodies start to
come back down to normal.  The IgA antibodies will usually drop back
to normal within a few of months; the IgG antibodies may come down to
normal within several months to a few years, and in some cases may
stay up indefinitely.  That does not mean that you still have active
CD (although in some cases these blood tests are used to monitor
compliance to the GF diet).
 
The antiendomysial antibody test is also about 90% accurate.  It is
more accurate in cases of people with more severe disease.  Celiacs
who have only minor changes on their biopsies will often have negative
antiendomysial test results.  It is also a bit more specific then the
antigliadin test.
 
A "sensitive" test is very likely to pick up cases of the disease it
is screening for, and very unlikely to miss cases.  A "specific" test
is very unlikely to be positive for any disease other than the one be
screened.  It turns out that the antiendomysial and antigliadin tests
are not specific to CD; there are other conditions that can yield
positive test results.  One of these is dermatitis herpetiformis (DH).
It turns out that about 90% of the DH patients either have CD or will
develop it.  These tests can also come back positive for a number of
conditions that are not related to CD.
 
There is a third test called the antireticulin antibody test.  It is a
little more specific than the antigliadin test, but is not as
sensitive so it is going to miss a lot of cases.
 
A physician may order only one of these tests, but generally we just
order all three of them.  These are helpful during the course of the
diagnosis; they help determine whether or not to proceed with a
gastroscopy or biopsy.  These tests can also be useful as
corroborative evidence in a patient with an intestinal biopsy
consistent with CD.  Some doctors also routinely repeat the tests on
annual basis.  Dr. Alexander does not routinely repeat the tests;
he'll order it when he sees some symptoms that make him suspicious of
active CD.
 
A third way to use the antibody tests is to screen relatives of a
diagnosed celiac for CD.  Somewhere between 2-10% (perhaps as many as
15%) of the people who have CD also have a first-degree relative with
CD.  So it makes sense to screen the first degree relatives (the
parents, siblings, and children of the celiac patient) for CD.  Once
you get beyond the first degree relatives, it is not generally
necessary to screen for CD unless, of course, there are symptoms
consistent with CD.
 
The other type of blood test to talk about is genetic testing.  This
is an area that has been evolving rapidly over the last few years.
One of the problems in this area is the nomenclature has changed so
that articles written five years ago use different terms than reports
written today.
 
The body has to identify foreign particles (bacteria, viruses, etc.)
and distinguish them from itself.  It does this through a series of
proteins that have certain configurations that will "fit" to certain
foreign molecules.  It is similar to a child's toy, a box with a set
of differently shaped holes; the idea is to have the child put the
correctly shaped object in each hole.  The body is genetically
programmed to make these "holes".  When a foreign particle floats
along and happens to fall into a matching hole, it sets off a complex
series of interactions that sets off the inflammatory process to kill
off this foreign invader.  This is determined through a class of
proteins called the "Human Lymphocyte Antigen (HLA)" system.  There
are different classes of this system, classes I, II, and III.  The
proteins that fit the class I antigens are present in virtually all
the cells in the body.  The class II antigens are the ones that are
involved with CD.  Of these there are two, DQB1*0201 and DQA1*0501
that encod e the DQ2 protein.  These are present in about 95% of
celiacs.  The other 5% have antigens that encode the DQ8 protein.  One
or the other of these genetic "markers" are present in nearly all
celiacs.
 
The HLA tests can be used to determine if you have the genetic markers
that are consistent with CD.  That does not mean you will get CD.
Even in identical twins, if one twin has CD only about 75% of the time
will the other have CD, so there are obviously environmental factors
involved as well as genetics.  About 30% of HLA-matched siblings of a
celiac will have CD.
 
Latent CD is another topic of interest.  This is CD that is "not
really here yet" or doesn't show up on a biopsy.  This is another area
of research that is still evolving.  There are different definitions
of latent CD.  It may be characterized by positive antibody test but
negative biopsies.  In these patients it is possible that five years
down the road repeat biopsies would then be positive and the disease
would no longer be latent.  It could be that antibody levels become
elevated before damage to the small intestinal villi occurs.