Sue Heathcote, 55, from Ayr, underwent an organ donation procedure known as kidney pairing to allow her sister-in-law Claire, 41, to receive a new kidney.
Paired donation is when a donor and recipient are incompatible but they are instead matched with another donor and recipient pair in the same situation and the kidneys are exchanged or swapped.
Claire Heathcote, a mother of two, has suffered from a form of kidney failure called Adult Polycystic Kidney Disease since birth.
In recent years her health began to deteriorate until last Christmas when her kidney function was working at only 8% of that of a healthy kidney. Unfortunately kidney dialysis was not a straight forward option and her family members were tested in the hopes of donating a kidney but were unsuitable matches.
She said: ". I was at a meeting with my doctor and we were discussing future treatment options. He mentioned 'kidney pairing'."
A computer in Bristol stores details of participating donors and recipients. Every three months it runs a check to see if any new donors match existing details on the register.
Sue said: "I was absolutely thrilled that I was able to register... in July last year Claire got a call to say that we had 'matched'. An altruistic donor had kindly donated to the 'pairing pool' and their kidney matched with Claire.
Sue added: "I had to take it easy after the operation and returned to work after about six weeks. I would appeal to everyone to consider kidney pairing. You only need one working kidney to survive."