Thank you for your query at AskTheDoctor.com
I understand your concern.
If your son already had a colonoscopy, then there is no need to get a lower gi x-ray or barium enema.
Barium Enema especially is recommended before a colonoscopy to check for any small bowel lesions, as they are highly sensitive in picking up small bowel diseases.
However, if a colonoscopy is already done, then there is no need to further get a barium enema done.
They are normally picked over colonoscopy because they are comparatively cheaper.
Hope this was helpful.
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