In a word: very. Yes, it’s crucial to consider the what ifs when contemplating something as important as living donation. And yes, later needing a transplant is more likely for a donor than it is for a healthy person who has never donated. But here’s the bottom line: there’s about a 1% chance on average of a living donor later needing a kidney transplant.
Apparently, that surprises people, particularly living donors. My post on the subject received the highest number of views of any of my posts. Needless to say, the news made a lot of people, including me (now nearly 15 years post donation), very happy and eager to share the good news.