Check your liver(s) first! Our female friend had issues with her livers failing, was on dialysis while on a list for a liver transplant. Her boyfriend offered one of his to her. At the hospital during a check to see if he was a suitable candidate, it was found that he was born with only one liver. Yep, it happens to some people. He could not be a donor candidate. Thankfully, our friend received a transplant liver from someone else and is doing well.
I think I meant kidneys, oh well.