Thank you for your reply.
I'm still living in Japan, so I'm uncertain how easily it will be to track down an AMA physician (American Medical Association, yes?)
I year or so ago, while undergoing tests at another hospital, I asked the doctor about the prospect of parasites in raw fish. The chap noted that his father was a fisherman, who had eaten raw fish for years, and had never once experienced parasites. Suffice to say, I didn't wish to question his judgement, and therefore never pursued tests.
However, you are right, a formal medical diagnosis would surely (?) indicate either way. I will try to discuss testing at the next hospital visit on Wednesday, although I expect the doctors there will wish to begin the colonoscopy preparations as soon as possible.
Thank you once again for your post.