I would ask yourself how important you consider your close friend. There is a small risk of something going wrong, you not waking up or you wishing later you had two kidneys if one goes bad for whatever reason. If he is the kind of friend that you would jump in front of a car to save him for, go for it. If he is a "friend" that you don't spend any time with except for drinking together once in 10 years, I'd advise against it.
I would ask yourself how important you consider your close friend. There is a small risk of something going wrong, you not waking up or you wishing later you had two kidneys if one goes bad for whatever reason. If he is the kind of friend that you would jump in front of a car to save him for, go for it. If he is a "friend" that you don't spend any time with except for drinking together once in 10 years, I'd advise against it.