CKD stages: what the G and A categories mean

How CKD is staged

Older descriptions of CKD used five stages based on kidney filtering alone. Current international guidance from KDIGO (Kidney Disease: Improving Global Outcomes) describes CKD in three parts, sometimes shortened to "CGA":

• C for cause: what is thought to be causing the kidney disease, such as diabetes or high blood pressure, where this is known.
• G for GFR: how well the kidneys filter, estimated as eGFR from a blood test.
• A for albuminuria: how much albumin, a protein, is leaking into the urine, measured with a urine ACR test.

Using G and A together gives a much clearer picture of risk than either number on its own.

G categories: based on eGFR

eGFR stands for estimated glomerular filtration rate. The lab calculates it from your blood creatinine using a validated equation that also uses your age and sex. It is reported in mL/min/1.73m², which adjusts for body size. Higher numbers mean better filtering.

An eGFR of 60 or above (G1 or G2) is not CKD on its own. CKD in these categories is only considered when there is another sign of kidney damage, such as albumin in the urine, lasting more than three months. Read more on the eGFR page.

A categories: based on urine ACR

ACR stands for albumin to creatinine ratio. It is measured on a urine sample, ideally the first urine of the morning. Some labs report ACR in mg/mmol and others in mg/g, so check the unit on your report before comparing it with the table.

A raised ACR can be temporary. Hard exercise, fever, a urine infection or menstruation can all push it up, so a raised result is usually repeated. See the urine ACR page.

Reading a stage such as "G3a A2"

If a doctor writes "G3a A2" in your notes, it means eGFR has been in the 45 to 59 range and urine ACR in the 3 to 30 mg/mmol (30 to 300 mg/g) range, on tests repeated over more than three months. The letters and numbers describe the results. They do not by themselves say what caused them or what will happen next.

Categories can change. eGFR can move up or down a little between tests, and ACR can fall or rise over time. Doctors look at the trend, not a single result.

The KDIGO risk chart ("heat map")

KDIGO publishes a colour-coded chart, often called the heat map. It places the G categories down the side and the A categories across the top. Each box is shaded from green through yellow and orange to red to show how the overall risk of problems, such as kidney disease getting worse or heart and blood vessel disease, changes.

The key idea is simple: risk rises as eGFR falls, and risk rises as ACR goes up. Two people with the same eGFR can have quite different risk if one has much more albumin in the urine. The table below describes the same pattern in words, so it can be read without relying on colour.

Doctors use this chart to help decide how often to repeat tests and when specialist input may help. It is a guide to risk across large groups of people. It cannot predict what will happen to one person.

Why only a clinician can stage CKD

Staging CKD is not something a lab report or a website can do for you. A clinician needs to:

• confirm that abnormal results have lasted more than three months, using repeated tests
• rule out short-term causes such as dehydration, infection, recent illness or some medicines
• judge whether eGFR is reliable for you. It can be less accurate in people with very high or very low muscle mass, during pregnancy, after an amputation, or during sudden illness
• consider your symptoms, other test results, scans and medical history, and look for the cause

If you have one eGFR or ACR result that falls into a category in the tables above, that does not mean you have CKD at that stage. Take the result to a doctor, who can decide whether and when to repeat it.

What to do next

If you have been given a CKD stage, it can help to ask your doctor what your G and A categories are, how often your tests will be repeated, and what you can do to lower your risk. Our page on monitoring CKD explains what is usually checked, and questions to ask your doctor can help you prepare. In Mombasa, many people bring results from a lab or hospital outpatient clinic to a general doctor first, who may later refer to a nephrologist if needed.

This page explains what a test or condition involves. It is not a diagnosis and does not replace advice from a doctor who knows your history. Your results should be interpreted together with your symptoms, other tests and a clinical assessment. Medical disclaimer.