It's kind of a catch 22.
But if you have a high deductible, and you have symptoms so this is being done as a treatment and not strictly preventative exam - I'm assuming you'd have to meet your deductible.
If you claim symptoms, it could impact your ability to get life insurance in the future.
My wife's mother was diagnosed with colon cancer at age 38 and was gone by the time she was 41. When my wife wanted to have a colonoscopy at age 40, the insurance said they wouldn't cover it. We ended up just paying for it - worth the peace of mind for her.