I had declining gfr over several years. I was told to hydrate before testing, but it kept going down. I went to see a nephrologist who tested me again, advising I over hydrate. My gfr came up from 42 to 60. I have read that you can test as many as 3 different times in a day and get different results each time. All I can say is drink more clear liquids. Keep a sipping class near you at all times. My creatine was on high end, but I take creatine regularly to keep sarcopenia at bay. We're all different. Best of luck on your quest.