CKD is diagnosed by the eGFR and other factors, and is divided into five stages.
 

Stage	Stage of Chronic Kidney Disease	eGFR ml/min/1.73 m
Stage1	The eGFR shows normal kidney function but you are already known to have some kidney damage or disease. For example, you may have some protein or blood in your urine, an abnormality of your kidney, kidney inflammation, etc.	90 or more
Stage2	Mildly reduced kidney function AND you are already known to have some kidney damage or disease. People with an eGFR of 60-89 without any known kidney damage or disease are not considered to have chronic kidney disease (CKD).	60 to 89
Stage3	Moderately reduced kidney function. (With or without a known kidney disease. For example, an elderly person with ageing kidneys may have reduced kidney function without a specific known kidney disease.)	45 to 59 (3A) 30 to 44 (3B)
Stage4	Severely reduced kidney function. (With or without known kidney disease.)	15 to 29
Stage5	Very severely reduced kidney function. This is sometimes called end-stage kidney failure or established renal failure.	Less than 15

Note: it is normal for the eGFR to change slightly from one measurement to the next. In some cases these changes may actually be large enough to move  the patient  from one stage of CKD to another and then back again. However, as long as the  eGFR is not getting progressively worse, it is the average value that is most important.