Many people first hear the words “stage 3 kidney disease” from a lab report or a quick comment at the end of a visit. It can sound alarming, and it often comes with little explanation. The staging system is actually fairly simple once you know it uses two numbers, not one.

This article explains how doctors stage chronic kidney disease (CKD), why the urine test matters as much as the blood test, and what the stage usually means for follow-up. It is general information; your own stage needs to be read alongside your history and earlier results.

CKD is common and usually silent. Using national survey data from 2021 to 2023, the CDC estimates that about 14 percent of US adults, roughly 37 million people, have CKD, and that about 9 in 10 adults with CKD do not know they have it. The CDC notes these estimates come from a single test and may run slightly high, which is exactly why repeat testing matters.

The international kidney guideline group, KDIGO, defines CKD as abnormal kidney structure or function present for at least three months. Its 2024 guideline classifies CKD by cause, by GFR category (G1 to G5) and by albuminuria category (A1 to A3). The guideline points out that the albuminuria half of this system is often missed.

The G stage: how well the kidneys filter

The G stage comes from your estimated glomerular filtration rate (eGFR), a blood test calculation that estimates how much blood the kidneys filter each minute. Our guide to reading eGFR, creatinine and UACR results covers how the number is made. The KDIGO categories, which the National Kidney Foundation also uses, are:

  • G1, eGFR 90 or higher: normal or high filtering
  • G2, 60 to 89: mildly decreased
  • G3a, 45 to 59: mildly to moderately decreased
  • G3b, 30 to 44: moderately to severely decreased
  • G4, 15 to 29: severely decreased
  • G5, below 15: kidney failure

One detail surprises many people: an eGFR in the G1 or G2 range does not count as CKD on its own. KDIGO is explicit that, without another sign of kidney damage such as albumin in the urine, neither G1 nor G2 meets the definition.

The A stage: what the urine shows

The A stage comes from the urine albumin-to-creatinine ratio (UACR), a test on a single urine sample. KDIGO’s three categories are:

  • A1, under 30 mg/g: normal to mildly increased
  • A2, 30 to 300 mg/g: moderately increased
  • A3, over 300 mg/g: severely increased

Albumin in the urine is often the earliest sign of kidney damage, and it can appear while eGFR is still normal. The National Kidney Foundation says plainly that both tests are needed for a clear picture of kidney health. We cover the urine test in more detail in protein in the urine: what a UACR test tells you.

Putting the two together

A full stage reads like “G3a A1” or “G2 A2.” The two parts together predict risk better than either alone. The KDIGO heat map, which the National Kidney Foundation reproduces in its CKD risk assessment card, colors each combination by the risk of CKD getting worse, of heart disease and of death. The same grid suggests roughly how many times a year to check eGFR and UACR.

The examples in the card show how this works in practice. Someone at G3a with normal urine albumin sits in a lower-risk box than someone at G3a with moderate albuminuria. Someone with an eGFR of 65 and persistent albuminuria can have CKD even though the eGFR alone looks reassuring. In general, the further down and to the right on the grid, the more often labs are repeated and the more treatment matters.

For people at G3 to G5, KDIGO also recommends using a validated risk equation to estimate the chance of reaching kidney failure over the next two to five years. That estimate helps decide when to involve a nephrologist and when, if ever, to plan for dialysis or transplant. Many people with early CKD have a very low risk.

What the stage changes

A stage is the starting point for a plan. The 2024 KDIGO guideline lays out several steps that apply across stages:

  • Confirm it. KDIGO advises repeating an abnormal eGFR or UACR to confirm CKD before acting on a single result.
  • Protect against albumin loss. ACE inhibitors or ARBs are recommended for many people with albuminuria, particularly A2 or A3.
  • Consider an SGLT2 inhibitor. KDIGO recommends this class for adults with CKD and an eGFR of at least 20 who have a UACR of 200 mg/g or more, or heart failure, and for people with type 2 diabetes and CKD. Large trials such as DAPA-CKD and EMPA-KIDNEY showed slower kidney decline with or without diabetes.
  • Control blood pressure. KDIGO suggests a systolic target under 120 when tolerated, using standardized office readings, with less intensive goals for people who are frail or prone to falls.
  • Keep sodium under 2 grams a day and avoid very high protein intake, ideally with help from a renal dietitian.
  • Review every medicine for kidney dosing, including over-the-counter products.

Treatment decisions depend on the whole person, so these are topics to raise with your own doctor rather than a checklist to apply alone. Our article on medicines and supplements that can strain the kidneys covers the last point.

The point of staging is to find the people whose kidneys are at higher risk early enough to change the course, and to give everyone else a sensible schedule for checking.

When to call a doctor

Call your doctor if a lab report shows a new drop in eGFR, a new albumin result of 30 mg/g or more, or if you notice swelling in your legs or around your eyes, foamy urine, or much less urine than usual. A sudden inability to pass urine, severe shortness of breath or chest pain needs emergency care: call 911.

Dr. Yana Shtern is board-certified in Internal Medicine and Nephrology, and labs are drawn in our office, so both numbers can be tracked over time in one place. You can read more about the practice’s approach on our kidney care page. If you have a stage on a lab report and would like it explained, a complimentary meet and greet with Dr. Shtern is an easy way to start.

This article is general information, not advice for your situation. Members can call the office with questions about their own care.