<<Disclaimer: Verify this information before applying it to your situation.>>

Recently I reported that at 6 months GF and three horrible gluten challenges
for endoscopic biopsies, I discovered that my initial blood tests screening
was a fiasco.  My allergist ordered the anti-gliadin antibody (AGA)-IgA and
IGG, anti-endomysial antibody (AEA)-IgA, and anti-tissue transglutaminase
(tTG)- IgA.  However, the lab did not inform my allergist that the AEA was
discontinued.  Then, the hospital reported the AEA in my records with no
results;  But, my allergist thought that the AEA and tTG were the same test
and reported them both negative.  Then, my Gastroenterologist also misread
the results as negative on all the tests.  According to Table 3 below, if I
was negative on both the AEA and AGA, CD is very unlikely.  However, if I
was positive on the AEA but negative on the AGA tests, CD is probable.  This
initial fiasco cast doubt over my whole impending diagnosis and I had to
endure gluten challenges which left me with the most severe symptoms, some
of which still haunt me each and every day as I struggle for full
restoration of my health.
The following quotes are from a medical review article called “Celiac
Disease.  Going Against the Grains” by M. Pietzak, C. Catassi, S. Drago, F.
Fornaroli, A.  Fasano.  Nutrition in Clinical Practice: 12/01; 16: 335-344.:
“AGA IgG has good sensitivity, whereas AGA IgA has good specificity, and
therefore their combined use provided the first reliable screening test for
CD.  Unfortunately, many normal individuals without CD will have an elevated
AGA IgG, causing much confusion among general practitioners.  However, this
test is useful in screening individuals who are IgA-deficient, because the
other antibodies used for routine screening are usually of the IgA class.
It is thought that 0.2%  to 0.4% of general population has selective IgA
deficiency, whereas 2% to 3% of individuals with CD are IgA-deficient.
Under these circumstances, the AGA IgG should be positive.  If a patient’s
celiac panel is positive only for AGA IgG, this is not highly suggestive for
CD if the patient is IgA-sufficient (corrected for age).  Markedly elevated
AGA IgG (i.e., greater than 4 times the upper limit of normal for that
laboratory) is highly suggestive of an enteropathy where the gut is more
permeable to gluten, such as parasitic infections, Chrohn’s disease,
allergic gastroenteropathy, and autoimmune enteropathy.  A strength of the
AGA antibodies is that they are ELISA tests and the results are independent
of observer variability.”

“The AEA IgA immunofluorecent antibody is an excellent screening test for
CD, with both a high sensitivity and specificity.  This antibody was
discovered in the early 1980s and rapidly gained use as part of a screening
‘celiac panel’ by commercial laboratories in combination with AGA IgG and
AGA IgA.  Its major drawbacks are that it may be falsely negative in
children under the age of 2 years, in patients with IgA deficiency, and in
the hands of an inexperienced laboratory.  Also, the substrate for this
antibody was initially monkey esophagus, making it expensive and unsuitable
for screening large numbers of people.  Recently, the human umbilical cord
has been used as an alternative to monkey esophagus.  However, the
subjective nature of the AEA assay may lead to false-negative values and
unacceptable variability between laboratories.”

“Because tTG had been first described as the autoantigen of CDE in  1997, it
has been used to develop innovative diagnostic tools.  The tTG IgA ELISA
test is highly sensitive and specific, using either the commercially
available guinea pig tTG or human recombinant tTG.  The tTG assay correlates
well with AEA-IgA and biopsy.  However, it represents an improvement over
the AEA assay because it is inexpensive and rapid (30 minutes), is not a
subjective test, and can be performed on a single drop of blood using a
dot-blot technique.  Therefore, this test is ideally suited for mass
screenings and in the future could be performed in the general
practitioner’s fooice, much like the now routine finger-stick hematocrit.”

“For the reasons outlined above, the IgA class human anti-tTg antibody,
coupled with the determination of total serum IgA, currently seems to be the
most cost-effective way to screen for CD.  AEA should be used as a
confirmatory, prebiopsy test, whereas AGA determinations should be
restricted to the diagnostic work-up of younger children and patients with
IgA deficiency, using the guidelines in Table 3.”

Table 3
Probability of CD based on three antibodies in combination

AEA IgA   AGA IgA   AGA IgG                Interpretation

+         +          +                     CD 99% probable
+         -          +                     probable
+         +          -                     CD probable
+         -          -                     CD probable
-         +          +                     CD less likely*
-         -          +                     CD less likely*
-         +          -                     CD less likely
-         -          -                     CD very unlikely+

*  If patient is IgA sufficient: AGA IgG > 100 warrants work-up of
enteropathy.
+  If patient is on a gluten-containing diet.
CD, celiac disease: AEA, antiendomysium antibodies: AGA, antigliadin
antibodies.





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