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Blood Screening and Celiac Disease, Dr. James Gregor
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Dr. Gregor is from the Department of Medicine & Epidemiology &
Biostatistics at the University of Western Ontario.
The prevalence of celiac disease (CD) overall is probably 1:1000, but
may be as high as 1:200 in some countries. (Prevalence refers to the
proportion of patients in any given population at a particular time
who have a condition.) CD is more common in Caucasians of European
descent.
Small studies have suggested a genetic association of CD with certain
immune markers and chromosomal abnormalities. This genetic link means
that first-degree relatives (siblings, children, parents) of a celiac
have a 4-8% chance of also developing CD.
CD is linked to various "autoimmune" diseases such as thyroiditis and
juvenile [Type I] diabetes, with prevalences up to 4%. Other
associated conditions include dermatitis herpetiformis (DH), IgA
deficiency, and lymphocytic colitis.
Dr. Gregor noted that one can find celiac disease (CD) by either an
empirical trial of the gluten-free (GF) diet, serologic testing, or a
small bowel biopsy. The trial, while not dangerous, does delay
diagnosis, is often not correct, and is difficult to use to rule out
CD. A trial also affects the quality of life and is expensive.
On the other hand, while a biopsy is the gold standard, it is
relatively expensive. And while a biopsy of a CD patient will show
villous atrophy, it is a differential diagnosis. There are other
diseases that also demonstrate villous atrophy such as tropical sprue,
lymphoma, Zollinger-Ellison syndrome, Whipples disease, eosinophilic
gastroenteritis, viral gastroenteritis and bacterial overgrowth.
Serological testing seeks to determine an immune-mediated antibody
response. Generally a test is considered to be good for screening
when both sensitivity and specificity are 90% or better. (Sensitivity
is a measure of the true positive results while specificity is a
measure of the true negative results.)
The antigliadin antibody (AGA) test looks at the interaction between
the immune system and the alcohol-soluble fraction of gluten. It is a
reasonably sensitive test but it tends to be positive with any sort of
gut inflammation so it is better at ruling out CD rather than
confirming it.
The antiendomysial antibody (EMA) test looks at IgA antibody reaction
against either monkey esophagus tissue or human umbilical cord tissue.
(The results are comparable for either tissue. For ethical and cost
reasons human umbilical cord is becoming the tissue of choice for this
test.) A qualitative immunofluorescent technique is used for this
test, which makes it highly-dependent on the skill of the operator.
Dr. Gregor's recommendations are to use the AGA and EMA tests for
screening and use a biopsy as confirmation.
Dr. Gregor then answered some questions:
Q: hould a celiac be biopsied every year?
A: No. A single follow up biopsy may be warranted, but not every
year.
Q: If you present with small bowel lymphoma or carcinoma, should
you be tested for CD?
A: Yes. In such cases about 1 in 4 are celiacs.
Q: Can the blood test be done on very young children?
A: Antiendomysial testing of a young child would not be reliable
until after the maternal antibodies were out of the child's
system. This can take 6-12 months or longer.
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