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I received 10 replies and the consensus was evenly split, 5 indicating
that 3-4 weeks of gluten ingestion was enough to go ahead with the
endoscopy and 5 indicating that the risk is high of getting a false
negative.  The latter 5 indicated that at least three months was
necessary and six was better.

Thank you very much for your responses.  She is going to talk this over
with her doctor.

Mary Carol