Agreed. You can take a blood test a day after training and be in apparent kidney failure, take the same test after a week off training and your kidneys are fine!eGFR is easily manipulated by exercise, diet, body composition, osmolality etc.
I had this many years ago when I got bloods done and forgot to not train for a few days.
Dr told me I was in kidney failure and then 1 week later, after a retest,told me I wasn’t
