I am a nephrologist and have some things to share which may help:
1) A eGFR is a number calculated from your blood creatinine, age and sex. Its intent is to give a better estimate of your true kidney function. However based on populations and may be incorrect patients. Your blood creatinine is by your muscle mass and therefore may overestimate or underestimate the eGFR. If your eGFR is in the lower than normal range it may not be CKD, it needs to be confirmed with further tests:
A blood Cystatin C is another way to estimate eGFR that is not affected by muscle mass.
a carefully done 24 hour urine for creatinine clearance can tell if your blood creatinine is slightly elevated because of having a higher muscle mass and therefore is not reflecting abnormal kidney function
Finally measuring urine albumin with a spot urine albumin to creatinine ratio will also indicate if you have kidney disease
if this cystatin C 424 hour urine creatinine clearance are normal and you don’t have an abnormal urine albumin/creatinine ratio very unlikely that you have CKD