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> Most of the responses have indicated oral entry whereas my doc
> suggested rectal.  Is this a standard practice?

I don't have any medical qualifications, but it sounds a long way
around - a probe would have to go through the rectum and all of
the large intestine to reach the small intestine. If the top of
the small intestine or duodenum was wanted the probe would have
to go through yards of small intestine too.

The oral route - throat, stomach, duodenum sounds much easier!
Your doctor might be planning another investigation as well though.

One doctor I went to after I had a GI infection on holiday wanted
to make sure I didn't have any blockages, and gave me what is best
described as a thorough examination. Every doctor has their own
preferences.

   Tim