<<Disclaimer: Verify this information before applying it to your situation.>>

This is not Medical advice

The biopsy determination of celiac disease requires demonstration of the
abnormalities in the proximal small intestine.   It is not possible to
get such a biopsy going through the anus.  The colonoscope does not
reach that far.   The biopsy instrument must go through the mouth.  This
is usually achieved with a upper endoscopy( AKA gastroscopy,EGD)
A colonoscopy is frequently preformed for the investigation of diarrhea
but does not and  can not detect celiac disease.

Joseph A. Murray MD
Coordinator, Celiac Disease Clinic
Associate Professor of Medicine,
University of Iowa
IA 52242