Chronic kidney disease stages: eGFR, ACR and what each stage means

Chronic kidney disease means the kidneys do not work as well as they should for a long period of time. The word "chronic" means long-term, and Kidney Care UK points out that it does not mean the condition is severe. The stage is a shorthand for how much kidney function remains and how much damage has been detected, and it helps your doctor decide how often to test you and which treatments to offer.

The NHS explains that CKD is diagnosed with blood and urine tests, and that the results can be used to tell the stage, a number that reflects how severe the damage is. NICE's guideline for England says adults should be classified using a combination of GFR and ACR categories, and notes that increased ACR and decreased GFR in combination multiply the risk of adverse outcomes.

The main test is a blood test that measures creatinine, a waste product. A doctor uses the result, along with your age, size and sex, to calculate an estimated glomerular filtration rate (eGFR), which the NHS describes as how many millilitres of waste your kidneys should be able to filter in a minute. Healthy kidneys should filter more than 90 ml/min.

NICE advises that an eGFR result below 60 in an adult who has not been tested before should be confirmed by repeating the test within 2 weeks, and that eGFR is less reliable in some situations such as acute kidney injury, pregnancy and muscle wasting disorders.

A urine test measures the albumin to creatinine ratio (ACR). The NHS says that alongside the eGFR, urine tests help give a more accurate picture of how well the kidneys are working, and the test also checks for blood or protein in the urine. Kidney Care UK explains that damage to the kidneys' filter system lets blood and protein leak into the urine.

The NHS gives three categories: A1 is an ACR of less than 3 mg/mmol, A2 is 3 to 30 mg/mmol, and A3 is more than 30 mg/mmol. NICE describes these as normal to mildly increased, moderately increased and severely increased. So a person whose results put them in G3a and A2 would be described as "CKD G3aA2".

NICE publishes a grid in which each combination of GFR and ACR category is labelled low, moderate, high or very high risk of adverse outcomes such as CKD progression, acute kidney injury and cardiovascular events. A person in G1 or G2 with a normal ACR is not considered to have CKD unless other markers of kidney damage are present, while G4 and G5 are very high risk in every ACR category.

NICE also says that management should not be determined by age alone, and that your GFR and ACR categories can be used to indicate your risk and discussed with you. The practical effect is that two people with the same eGFR can be advised differently, depending on how much albumin is leaking and what other conditions they have.

NICE sets out the minimum number of eGFR checks a year for each combination. For example, it suggests 0 to 1 per year for G1 or G2 with A1, 1 for G3a with A1 or A2, 2 for G3a with A3, 2 or more for G3b with A3, and 4 or more for G5. NICE stresses that the frequency should be agreed with you and tailored to the cause, the rate of change, other risk factors such as diabetes or heart failure, and changes to medicines.

The NHS says that people at higher risk of CKD, for example those with high blood pressure, diabetes, cardiovascular disease, a family history of kidney disease or who take long-term medicines such as lithium, omeprazole or NSAIDs, should have regular testing, because early CKD often has no symptoms.

There is no cure for CKD, the NHS says, but treatment can relieve symptoms and stop it getting worse. This includes lifestyle changes, medicine to control associated problems such as high blood pressure and high cholesterol, medicines that help the kidneys keep working for longer, and, in advanced CKD, dialysis or a transplant. NICE's guideline also mentions SGLT2 inhibitors as options for some adults with CKD.

Kidney Care UK says most people in stages 1 to 3 manage the condition with support from their GP without specialist kidney care, and that people whose CKD progresses to stage 4 are referred to a kidney doctor (nephrologist). NICE gives more detailed criteria for referral of adults, including a sustained fall in eGFR of 25% or more with a change in category, a sustained fall of 15 ml/min or more in a year, an ACR of 70 mg/mmol or more, and poorly controlled blood pressure despite at least four medicines.

The NHS says CKD only progresses to kidney failure in around 2 in 100 people with the condition. It also warns that even mild CKD increases the risk of cardiovascular disease, such as heart attack and stroke, which is why blood pressure and cholesterol control matter so much.

The NHS suggests lifestyle changes that help to keep you as healthy as possible and prevent CKD getting worse, and regular check-ups to monitor your condition. If you take medicines that can affect the kidneys, such as NSAIDs, it is worth asking your GP or pharmacist whether they remain suitable once you know your stage.

A diagnosis of CKD can feel alarming, particularly if you see a stage number. Remember that the stage is a snapshot, and that for many people the numbers remain stable for years.