eGFR is an indirect measurement of kidney function. It can be slightly lower in some people with normal kidney function for various reasons.
There are additional kidney function tests that would be used for a more complete picture of kidney function if it was suspected that you had a kidney condition. There are more direct GFR tests, minus the ‘e’ prefix which means estimated. However, a better blood test that is more accessible would be Cystatin C. Worth getting one of those as a baseline at some point.
In the content of donation, though, it’s not worth risking it. It’s best to play it safe. If you happened to have been inspired by the kidney donation story and blog that circulated in rationalist communities, it’s also worth noting that it was not a great source of information about the relative risks of the procedure, despite being presented as comprehensive and well researched.
The first time I tried a community donation, they didn't do that. But a couple years later one of my brothers needed a kidney, so I got tested again. Again, my eGFR was low 70s, and so they did the Cystatin C test. I scored 1.00 (ref range 0.52-1.23mg/mL) which they mapped to an eGFR of 78, and I was rejected.
None of my other siblings were a good enough match, so one of my sisters donated hers (IIRC, her eGFR was low 90s) as part of a chain. That was more than two years ago and my sister is feeling fine. My brother is no longer on dialysis, though he didn't experience one of those feel-good stories where he got his kidney and he suddenly felt amazing, unfortunately.
[EDIT] I forgot to address the last part of your comment. A few years back an email acquaintance of many years mentioned that he is on dialysis. Although he is in Germany, I said if he can't find a donor, I'd be willing to fly there to donate directly if I matched or to be part of a chain. He is in Germany and his response surprised me: thank you very much, but he said living donations were not allowed (at least from non-relatives). Maybe things have changed, this was back in 2016.
"But there are some reasons that make this solution unlikely. At first I am very sure that this kind of donor isn't allowed in germany. We have strong ethic rules regarding donation by living people because of the bad experiences with commercial organ deals."
Still the idea sat with me. I have donated many gallons of blood and 25 years ago signed up for "be the match" marrow donation that never came to anything, though every few years they send a confirmation letter to make sure my address is still valid. It most charity donations I can write a check and there is a diffuse sense that maybe I incrementally did some good, but giving a kidney has a high probability to make one person's life dramatically better. So that was my motivation.
There are additional kidney function tests that would be used for a more complete picture of kidney function if it was suspected that you had a kidney condition. There are more direct GFR tests, minus the ‘e’ prefix which means estimated. However, a better blood test that is more accessible would be Cystatin C. Worth getting one of those as a baseline at some point.
In the content of donation, though, it’s not worth risking it. It’s best to play it safe. If you happened to have been inspired by the kidney donation story and blog that circulated in rationalist communities, it’s also worth noting that it was not a great source of information about the relative risks of the procedure, despite being presented as comprehensive and well researched.