I exercise 5 days a week for 60 to 75 minutes (spinning class and then resistance training). I am 50. The last three years my creatinine level is slightly high and eGFRis slightly low. When I work out, I always sweat a lot and the smell is ammonia like. My blood pressure is normal; always less than 120/80.
I have a similar situation. I am also 50 with normal blood pressure and weight. I had a routine physical exam during training for a half marathon (not an elite runner by any stretch) and they referred me to a nephrologist because my serum creatinine was above 1.0 giving me a GFR in the 50s. When I anxiously went to the nephrologist he laughed and said that the test is not very informative for an active female. The key was that I didn’t have any albumin in my urine and also had high urine creatinine. We are just producing more muscle waste and are chronically dehydrated from exercise. My opinion is that as long as you don’t have albumin in your urine, you are fine. Keep up the great exercise routine, and drink lots of water.