Dear Terry,
I don't know enough to say anything particular about your specific GFR status. However, I will tell you that, twice in the last few months (once was last week), I got some less-than-perfect lab results and was extremely upset. Not only have I poured a lot of time and effort into the whole long process of being approved to donate (this has been going on over one year), but I have somebody now depending on me, waiting/hoping for me to help him out by donating.
In the first instance (blood pressure higher than normal), I was upset enough to schedule an appointment with my regular doc, and he simply pooh-poohed the results as really only trivially elevated, and of no real significance. Indeed, since then my pressure readings have been normal, thankfully.
The second instance involved a possible elevation in glucose, and some protein in my urine. Since then, the "do-over" data have been perfectly normal (though there are still a couple of test results not yet back from the lab).
I wish you the same luck--sometimes, imperfect results could prove to be a random one-time thing.
However, having said that, I would venture to say that one really should be pretty darn sure of a nice good GFR status before donating a kidney. It has been drilled into me that, however many nephrons you have working away now in your two kidneys, you will have only half of them after donation.
Yes, the remaining kidney ends up doing more of the work, etc. Still, make sure that the test is re-done, and interpreted carefully. You can also ask what the phrase "borderline" really means. Is it set artificially high or low for some reason?
Overall, though, based on my own experiences, it's not worth getting overly upset at least until you can sit down with a competent medical professional who has the time to carefully explain what's really going on.
Good luck, Snoopy