You know you make new blood, and people donate blood regularly? Apart from small slices of liver, your organs don't really regrow. You could donate/sell one of your kidneys, but we now know there are negative long-term effects of that.
"Compared to the general public, most kidney donors have equivalent (or better) survival, excellent quality of life, and no increase in end-stage kidney disease"
https://nhsbtdbe.blob.core.windows.net/umbraco-assets/1433/1... [PDF, page 7]
To know if there is an effect, you need to not compare to the general public, but to a subset similar in factors which are associated with the outcome measures to kidney donors.