Dear "Jonesdonor",
I'm not a medical professional either, but have read a lot since donating a kidney 14 years ago, at age 56 (I'm 70 now). One thing that I learned is that the GFR # we usually get is the "estimated GFR" (eGFR). To get the more exact reading of the GFR a more complicated and expensive test is done, and there can be a big difference between the "estimated" GFR and the real one.
A doctor who is also a kidney donor once explained on this site that while some doctors look at a number (GFR or creatinine), check a chart, and then declare "kidney disease!", other doctors look at the whole person and consider the test numbers as one among many important indicators, as noted in the postings above.
I'm in Japan now, and consulted a kidney specialist here a couple of years ago (with the help of a fluent translator). Although my eGFR has been in the 40s for the past 5 years, the kidney specialist (like my previous doctors) was not greatly concerned, taking into consideration my lack of one kidney, my age, and the general physical examination. As far as how I feel, I still run a half-marathon or two each year (and was running full marathons until I got too slow a few years ago. I do my work and feel fine.
So (as far as I know) it is very good to be watchful and concerned, and take good care of yourself (diet, exercise, etc.) What the GFR numbers actually MEAN for me is still something of a mystery to me.
Clark, I remember a few years back that there was a long and very informative conversation on GFR, with lots of clear explanation for a doctor/donor. I could not locate it myself now. Could you possibly find it for "Jonesdonor"? I remember that it was very informative (to me at least).
best wishes,
Fr. Pat