The stages of chronic kidney disease, and what they mean in practice

What chronic kidney disease actually means

KDIGO, the international kidney guideline body, defines chronic kidney disease as abnormalities of kidney structure or function, present for more than three months, with implications for health. Every part of that sentence earns its place.

More than three months is what makes it chronic, as opposed to acute kidney injury, which comes on suddenly (through dehydration, infection or a medicine, for example) and is often reversible. A single abnormal blood test is not chronic kidney disease. It is a reason for a second test.

Structure or function means the damage counts even when the filtration rate looks fine. Someone with heavy protein leaking into the urine and a perfectly normal eGFR of 95 still has chronic kidney disease. This surprises people, and it is why the urine test matters.

The three-part diagnosis: cause, filtration, albuminuria

KDIGO classifies kidney disease by Cause, GFR category and Albuminuria category, which clinicians shorten to CGA. It is a genuine improvement on the older habit of quoting a stage number alone, and it changes what your stage means.

The filtration categories, G1 to G5

These describe how much blood your kidneys filter, estimated in mL/min/1.73 m2. Here is what each one means, and what it usually means for your life rather than for your chart.

G1eGFR 90 or above

Normal or high filtration.

This is only chronic kidney disease if there is another sign of kidney damage, such as protein in the urine. If there is, it is real, and it is worth treating early, because this is the stage where the most can be changed.

G2eGFR 60 to 89

Mildly reduced filtration.

Again, only CKD if there is another marker of damage. Many people live an entire life at this level and never come to harm. The work here is blood pressure, diabetes control, and knowing your ACR.

G3aeGFR 45 to 59

Mildly to moderately reduced.

Usually still no symptoms at all. This is the stage most often found by accident on a routine blood test. It is not a sentence: most people at G3a never need dialysis. It is a signal to protect what you have.

G3beGFR 30 to 44

Moderately to severely reduced.

Anaemia, bone chemistry and blood pressure need active attention now. Referral to a kidney specialist is often considered around here, especially if albuminuria is high or the number is falling.

G4eGFR 15 to 29

Severely reduced.

This is the stage where planning begins in earnest: understanding the treatment options, considering transplant referral, and preparing an access if haemodialysis is likely. It is not the stage where dialysis starts.

G5eGFR Below 15

Kidney failure.

Kidney failure, which is not the same thing as being on dialysis. Many people live at G5 for months or years without it. The decision to start is driven by how you are, not by crossing this line.

Two things about this table are routinely misunderstood, and both are worth saying plainly.

• G1 and G2 are only chronic kidney disease if something else is wrong too: albuminuria, blood in the urine, an abnormality on a scan, an abnormality on a biopsy, a tubular disorder, or a history of transplant. A normal person with a normal eGFR of 95 does not have "stage 1 kidney disease".
• G5 is not dialysis. People receiving dialysis are designated G5D. G5 on its own means the filtration rate is below 15, and a great many people live there, monitored and treated, for a long time before anything changes.

The albuminuria categories, A1 to A3

This is the half of the diagnosis that patients are least often told about, and it is the half that most often predicts what happens next. It comes from a urine test, the albumin-to-creatinine ratio, ideally on an early-morning sample.

Risk, not stage: what the guidelines now recommend

This is a real and fairly recent shift, and it is good news for anyone who has been staring at a number in fear. KDIGO 2024 recommends using a validated risk equation (in practice, the Kidney Failure Risk Equation, or KFRE) to estimate the actual probability of kidney failure over the next two to five years in people with G3 to G5 kidney disease.

In other words: the question is no longer "what stage are you?" but "what is your risk, and what should we do about it?" The thresholds KDIGO cites are:

• Referral to a kidney specialist: consider it when the five-year risk of kidney failure is roughly 3 to 5% on a validated tool, or when the eGFR is below 30, or when the filtration rate has fallen by 20 to 30% or more and stayed down.
• Starting to plan for treatment: KDIGO suggests planning for a pre-emptive transplant and/or dialysis access when the eGFR is below 15 to 20, or when the two-year risk of needing kidney replacement therapy is above 40%.
• In the UK, NICE advises starting the assessment for dialysis, transplant or conservative care at least a year before the treatment is likely to be needed.

Notice what those thresholds are for. They are triggers for conversations and preparation, not for starting dialysis. Preparing for something is not the same as needing it, and a fistula created in good time is a fistula that is ready if it is ever wanted. The alternative, arriving in hospital needing dialysis this week, with no access and no plan, is a genuinely worse experience, and it is common enough that clinicians have a name for it.

What the stage does not tell you

• It does not tell you how you feel. Symptoms and eGFR correlate loosely at best. People at G4 often feel entirely well; some people at G5 feel dreadful and some feel fine.
• It does not tell you the speed. An eGFR of 25 that has been stable for six years is a very different situation from an eGFR of 25 that was 45 last year. Your team is watching the slope, and so should you.
• It does not tell you the cause. Kidney disease from diabetes behaves differently from polycystic kidney disease, which behaves differently again from a glomerular disease. In Seychelles, most kidney failure follows hypertension and diabetes, but polycystic kidney disease is a notable local contributor, and it is inherited.
• It does not decide when dialysis starts. That is a separate decision, driven mostly by symptoms, and we have given it its own guide.

The most useful thing you can do with your stage is to stop reading it as a countdown and start reading it as a to-do list: control your blood pressure, control your diabetes if you have it, know your ACR, keep your appointments, protect your veins if dialysis is a possibility, and ask about transplant referral early rather than late.