I have fluctuations between 35 and 55. The creatinine based eGFR is affected by hydration and muscle loss, as well as low blood pressure and low heart ejection fraction, according to my nephrologist. I will echo the other poster and suggest the Cystatin C GFR which is steadier.

I didn't worry about "stage 3" in the 50's for eGFR. When I hit 36 I got a nephrologist! Cystatin C was reassuring and remained in the low 50's.

Hydrate before any creatinine based eGFR's!