ENKIKnowledge libraryCKD basics
CKD stages explained
CKD is classified using both estimated filtration, called the G category, and urine albumin, called the A category. A stage is useful shorthand, but it does not describe the whole person or predict an exact outcome.
This guide helps you understand terms and prepare questions. It cannot diagnose a condition or tell you to change treatment. Seek local medical care for urgent or severe symptoms.
Start here
Three points to keep
- G1 and G2 require another persistent marker of kidney damage to count as CKD.
- A lower eGFR and a higher urine ACR generally mean higher risk.
- Trend, cause, age, other conditions, and treatment response also matter.
The eGFR categories
The G category is based on eGFR in mL/min/1.73 m². Boundaries help standardize care, but a result close to a boundary should not be overinterpreted.
| Category | eGFR | General description |
|---|---|---|
| G1 | 90 or higher | Normal or high filtration |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | Below 15 | Kidney failure |
The albuminuria categories
Urine albumin-to-creatinine ratio, or ACR, adds important information that eGFR cannot provide. Units vary by country, so compare the result with the unit printed by the laboratory.
| Category | ACR mg/g | ACR mg/mmol | General description |
|---|---|---|---|
| A1 | Below 30 | Below 3 | Normal to mildly increased |
| A2 | 30–300 | 3–30 | Moderately increased |
| A3 | Above 300 | Above 30 | Severely increased |
Why both categories matter
A person may have a relatively preserved eGFR but substantial albuminuria, or reduced eGFR with little albuminuria. These patterns can carry different risks and may point toward different causes.
Clinicians combine G and A categories with the cause of CKD to estimate the chance of progression, cardiovascular events, and complications. One result is not a countdown to dialysis.
Stage changes and trends
Small movements can occur because of hydration, illness, medicines, laboratory variation, or normal biological variation. A sudden fall may represent an acute kidney injury and should not simply be relabeled as a new chronic stage.
The most useful view is a sequence of comparable results over time, interpreted alongside urine albumin and clinical events.
What changes in follow-up
CKD requires abnormalities of kidney structure or function for at least three months; it does not require both eGFR and uACR to be abnormal or identical at every test. G1 and G2 need another persistent marker of kidney damage.
eGFR and urine albumin are checked at least annually in CKD and more often when risk is higher or treatment changes. G3-G5 may require checks for anemia, potassium, acid balance and bone/mineral problems. Timing is individualized using cause, G and A categories and trends.
With severely reduced kidney function, discuss dialysis, transplant evaluation and comprehensive conservative care early. G5 does not automatically mean starting dialysis: symptoms, laboratory results, quality of life and preferences matter, not a single number.
Practical steps at any stage
Review blood pressure, diabetes and appropriate kidney-protective medicines with your team. Avoid self-treating with NSAIDs such as ibuprofen or naproxen. A dietitian can tailor salt, protein, potassium and phosphorus advice to your results; blanket restrictions do not fit everyone.
Ask for a sick-day plan and confirm what to do if you cannot eat or drink. Do not stop or change medicines on your own. Not smoking, staying active within your abilities and keeping follow-up appointments also matter.
When to get help
A sudden eGFR fall may be acute kidney injury and needs assessment, not simply a new chronic-stage label. Contact your team the same day for a large unexpected change, much less urine, rapidly increasing swelling or persistent vomiting.
For your next visit
Questions worth taking with you
- 01What are my current G and A categories?
- 02Is the change large enough to be clinically meaningful, or should it be repeated?
- 03What does my combined risk category mean for follow-up?
Common questions
Clear answers to common searches
What CKD stage is an eGFR of 45?
An eGFR of 45 mL/min/1.73 m² is in G3a (45-59), not G3b (30-44). One result alone does not confirm CKD: duration, trend, urine albumin and clinical context matter.
What is the difference between CKD stage 3a and 3b?
G3a covers eGFR 45-59 and G3b covers 30-44 mL/min/1.73 m². G3b generally carries higher estimated risk, but urine albumin, cause, trend, age, and other health factors also matter.
What does G3a A2 mean?
G3a describes an eGFR of 45-59, while A2 describes moderately increased urine albumin. The combination helps clinicians estimate kidney and cardiovascular risk and plan follow-up.
Can a CKD stage improve?
eGFR can improve when a cause is treated or a temporary decline resolves. Chronic scarring usually does not reverse, and small fluctuations do not prove recovery or permanent deterioration. Follow the trend with your team.
Does G5 mean dialysis must start immediately?
No. G5 means eGFR below 15, but starting dialysis depends on symptoms, laboratory findings, overall health and preferences. Plan with your nephrologist rather than waiting for a crisis.
Evidence trail
Sources
ENKI prioritizes current clinical guidelines and public-health sources. Links open on the publisher's website.
Published by the ENKI Health Editorial Team under our editorial policy.