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Re dependability of antibody tests to rule out celiac disease as a
possibility in a family member of a celiac, who has symptoms that are
suggestive of CD.  The antibody are occassionally wrong.  This happens in
the best of labs and is related to natural variation or IgA deficency!!.
It has been my practice to advise consideration of biopsy in family
members who have symptoms.  Measuring IgA levels might indicate IgA
deficiency state which would indicate a possible reason for the negative
test. There would be a variation on one of the tests that could be done
on the blood sample if the patient was IgA deficient that we have found
helpful.  That is to do the IgG endomysial antibody test, which is often
positive in IgA deficient patients who have celiac disease.  Nothing in
medicine is perfect, even biopsies which are subject to interpretation
and sampling problems. Joe murray