When we talk about the donation of organs it is acceptable.
It is Christian way to share value and help save a brother. God made his life for us by dying on the cross. Our life should be a reflection of, sharing and caring for one another. If we can give life to our brothers then we can be saved.
The same man can live by only one kidney and if you're in that position where we are kind enough to help a brother or we have that willing heart to help one another then we can as well save the life of one another. it can be our children, our wives, our family members.
It is very pleasing to give and care for one another as a believer.