So, a family member or a close friend needs a transplant and you generously offer to be a donor. But you are simply not a good match as donor, and the transplant gets delayed.
Meanwhile, 30 miles away, another recipient / donor pair have just been told that the donor is not a match, and they too have the transplant delayed. But it just so happens that you are a perfect match for this patient. And the donor in the second pair is a perfect match for someone 50 miles away in a similar situation. What if the potential donor for this third patient was a great match for your family member of friend? A three way swap would enable all three patients to get a new kidney. Not from their original generous friend or family member, but threw their willingness to help.
This is a network transplant, and it doesn't just apply to kidney patients either.
But how do these three patients and donors meet up? By chance? Highly unlikely, isn't it. So transplant networks exist, where patients and donors register and help each other. If you are willing to donate to save a friend or family member, ask your doctor about this concept. Don't just say, oh, I can't help him / her as I'm a poor match, so we'll give up now.
If you live in the US , check out this page at the National Kidney Foundation website.
UK Law was changed in 2004 to make such network transplants legal, as discussed in this article from the BMJ.
Live somewhere else? Just ASK about this.