Can your GFR level also mean your percentage of kidney function?

Close. They are not the same, but close. Since a normal gfr-glomerular filtration rate-is about 100ml/minute, the % term is often used. So a GFR of 30 cc/min is about 30% of normal kidney function. As one ages, the GFR naturally decreases, so it becomes less accurate. But for common use they are about the same.