The intersection of "your neighborhood has lots of lead in it" and "you flunked an inaccurate test" probably has a lot fewer false positives in it, right? You were exposed to lead. You might have lead poisoning, we can't be certain, but you're categorically in danger of getting it, based on environment and/or behaviors.

Note, I'm talking about UK guidance. Possibly they're missing some cases, but they do have a program of nationwide testing to monitor if there's any issues and the NHS has a direct financial incentive to report it and get it fixed via prevention if it's an issue.