Sounds like it does in fact have a bunch to do with the base rate fallacy.

I suppose that's fair way to look at it, but people are being left with the impression that the problem is inherent in the tests, when the problem is entirely separate from the tests themselves.

I suppose it's a fair way to look at it, too! It's good when we can reach a shared understanding of what's happening; so often, the dynamics of message boards work against that.

Most people aren't going to be happy with "the scan shows something unusual that would normally be concerning, but you say you feel fine so I'll trust you instead of the scan".