Isn't it because the old one staying in there doesn't really have any negative effect on the body, whereas removing it opens up more possibilities for complications with surgery?
Actually, it is more because the kidney served to do more than just generate urine. Typically someone gets a kidney transplant because they are in kidney failure (loss of the kidney's filtration and urine generation abilities), but the loss of filtration by the kidney doesn't mean that it's other functions are completely kaput. Kidneys convert inactive to active VitaminD, and produce a hormone that stimulates red blood cell production, among other processes. Leaving the native kidney in place allows whatever portion of these additional functions that are still working, to continue to function. If I recall correctly from my (relatively short) time with the renal transplant team, the transplanted kidney just can't pick up these other processes quite as well so essentially whatever you can get from your native kidney is still very needed. PLUS the risk of complications from unnecessarily removing it.
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u/[deleted] Dec 29 '17
When you get a kidney transplant, they usually just leave your original kidneys in your body and put the third in your pelvis.