I believe you can't ever get cleared. The only way to confirm mad cow is to dissect the brain, so obviously it can't be tested for in a living person. As a result, anyone with over a certain amount of risk for mad cow can never be allowed to donate.
The surgeons second line was "don't worry we have really good drugs for HIV these days"
In the end we agreed that given my age and I then had fairly good function left that letting some on else have it was for the best