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I have an acquaintance who runs a pathology lab in New Delhi.  I asked him
how he tests people for Celiac disease.  He told me he does a test where a
person in fasting state takes some compound? and then measures the volume
and concentration? of the compound in the urine.  I was jet lagged at the
time I asked him so the details of the test are no pretty foggy.  Could one
of our experts clarify the nature of this test for me?