system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If someone donates a kidney and the recipient dies a few years later, can the original donor get their kidney back?

Would a donor's body recognize their own organ if it was re-transplanted into their body? Is it even a good idea, or would the risk of major surgery outweigh the benefit of having your kidney back?
gpt
The transplanted kidney would have taken damage from being transplanted in another person's body. The person who gave the kidney would have had their other kidney get bigger to compensate for the loss of one of their kidneys. There would be little to no benefit/ probably a lot more harm in trying to give back the kidney even if it was okay because the person who gave it has already had enough changes to make up for it. You would not want to give it back due to things like fibrosis(scar tissue), etc. Also when you transplant a kidney you put it in a different place than where you take it(in the pelvis area). So it's not like you can just "put it back."

On a side note, kidneys are VERY easy to damage, so depending on what they die from it would probably not be able to be used anyway even if it were possible.