A patient is said to have chronic kidney disease (CKD) if they have abnormalities of kidney function or structure present for more than 3 months. The definition of CKD includes all individuals with markers of kidney damage (see below*) or those with an eGFR of less than 60 ml/min/1.73m2 on at least 2 occasions 90 days apart (with or without markers of kidney damage).
*Markers of kidney disease may include: albuminuria (ACR > 3 mg/mmol), haematuria (or presumed or confirmed renal origin), electrolyte abnormalities due to tubular disorders, renal histological abnormalities, structural abnormalities detected by imaging (e.g. polycystic kidneys, reflux nephropathy) or a history of kidney transplantation.
CKD is classified based on the eGFR and the level of proteinuria and helps to risk stratify patients.
Patients are classified as G1-G5, based on the eGFR, and A1-A3 based on the ACR (albumin:creatinine ratio) as detailed below:
- A person with an eGFR of 25 ml/min/1.73 m2 and an ACR of 15 mg/mmol has CKD G4A2.
- A person with an eGFR of 50 ml/min/1.73 m2 and an ACR of 35 mg/mmol has CKD G3aA3.
It is important to note that patients with an eGFR of >60 ml/min/1.73m2 should not be classified as having CKD unless they have other markers of kidney disease (see above*).
GFR category G2 may be over-diagnosed by eGFR because equations used to estimate GFR may give falsely low results in people with near-normal function. See measurement of renal function
Patients with CKD can be classified depending on their level of kidney function, or eGFR, and the amount of protein present in the urine. This information forms the basis of CKD staging which is useful for planning follow up and management. The higher the stage (G1->G5) and the greater the amount of protein present in the urine (A1->A3) the more “severe” the CKD.