At a glance
- eGFR estimates filtration; urine albumin looks for leakage. Guidelines advise testing both.
- Chronic kidney disease needs changes lasting at least three months, so unexpected results are usually repeated.
- Muscle mass, illness and the equation used can shift eGFR; compare results with the same units and method.
01
Two tests, two different questions
Kidney checks usually combine a blood test and a urine test because they measure different things. The estimated glomerular filtration rate (eGFR), calculated from a blood creatinine result, estimates how well the kidneys filter. The urine albumin-to-creatinine ratio (UACR) looks for albumin, a protein that leaks into urine when the kidney filters are damaged. The KDIGO 2024 international guideline advises testing people at risk with both, because one can be abnormal while the other looks normal.
One result on its own is not a diagnosis. KDIGO defines chronic kidney disease as abnormalities of kidney structure or function present for at least three months, and it advises repeating tests to confirm an unexpected low eGFR or raised albumin before drawing conclusions. This guide explains the labels and categories on a report so you can discuss them; what they mean for you depends on your history, other results and your clinician's assessment.
02
Labels you may see on the report
Laboratories format reports differently. Use the table to match each label to what it measures, then ask about anything that does not fit.
| Label | What it describes | What to clarify |
|---|---|---|
| Creatinine (blood) | A waste product made by muscle and removed by the kidneys; the starting point for most eGFR results. | Was this a routine test or taken during an illness? |
| eGFR, mL/min/1.73 m² | An estimate of filtration calculated from creatinine with an equation; not a direct measurement. | Which equation did the laboratory use? |
| eGFRcr-cys or cystatin C | An estimate that adds a second blood marker, cystatin C; the NIDDK describes the combination as more accurate than creatinine alone. | Would a cystatin C test help in my situation? |
| UACR, mg/g or mg/mmol | Albumin in a urine sample compared with urine creatinine, which corrects for how concentrated the urine is. | Which unit is shown, and has the result been repeated? |
| Urine protein-to-creatinine ratio, g/gCr | Measures all protein rather than albumin; used in Japan when an albumin test is not available. | Which test was done, and how does it compare with earlier ones? |
The equation matters when you compare results from different places. The NIDDK recommends the 2021 CKD-EPI equations, which do not use race. The Japanese Society of Nephrology uses equations developed for Japanese people (JSN eGFRcr), because the CKD-EPI equation overestimates kidney function in Japanese adults.
03
How the categories work
Guidelines describe kidney results with two sets of categories: one for filtration (G1 to G5) and one for albumin in urine (A1 to A3). Together with the cause, they make up the CGA classification. These are definitions used by clinicians, not targets to reach or a self-diagnosis tool.
| Category | Range | Guideline description |
|---|---|---|
| G1 | eGFR 90 or more | Normal or high |
| 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 |
| A1 | UACR below 30 mg/g (below 3 mg/mmol) | Normal to mildly increased |
| A2 | 30 to 300 mg/g (3 to 30 mg/mmol) | Moderately increased |
| A3 | Above 300 mg/g (above 30 mg/mmol) | Severely increased |
Risk depends on both numbers together. KDIGO's risk chart rates G1 or G2 with A1 as low risk when there are no other markers of kidney damage, in which case the person does not have chronic kidney disease. Higher albumin categories raise risk at every eGFR level. In Japan, where urine protein is often measured instead, the JSN guideline treats a protein-to-creatinine ratio of 0.15 g/gCr or more, roughly equivalent to an albumin ratio of 30 mg/gCr, as an important sign of kidney damage.
04
Why results change, and why trends matter
Every eGFR equation carries some imprecision, and the NIDDK stresses that eGFR is an estimate. Creatinine comes from muscle, so the JSN guideline notes that eGFR can read high in people with low muscle mass, such as after long bed rest, and low in athletes or very active older adults. Diet and exercise can also affect creatinine. Cystatin C is less affected by muscle, but thyroid function, smoking, inflammation and some medicines influence it.
That is why a single result is usually confirmed and then followed over time. The NIDDK notes that a raised urine albumin test may be repeated once or twice to confirm it. Keep copies of earlier reports with their dates, units and the equation used, so a change can be judged against the same yardstick. People with diabetes are advised by the NIDDK to have kidney checks every year; how often anyone else is tested is a decision for the care team.
05
Questions to bring to the appointment
Bring your recent and earlier reports, your medicine list and any results from other clinics. These questions help turn the numbers into a shared understanding.
- Which eGFR equation and which urine test were used, and in what units?
- Does this result need to be repeated to confirm it?
- How do my eGFR and urine albumin look together, compared with earlier results?
- Could my muscle mass, a recent illness or a medicine affect these numbers?
- Would a cystatin C test add useful information for me?
- When should these tests be checked again, and what result would change the plan?
Sources
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease (Kidney International 105(4S))Kidney Disease: Improving Global Outcomes (KDIGO) · 2024Source accessed:
- Estimating Glomerular Filtration Rate: GFR equationsNational Institute of Diabetes and Digestive and Kidney Diseases · 2025Source accessed:
- Chronic Kidney Disease Tests & DiagnosisNational Institute of Diabetes and Digestive and Kidney Diseases · 2016Source accessed:
- エビデンスに基づくCKD診療ガイドライン2023 第1章 CKDの診断と重症度分類Japanese Society of Nephrology · 2023Source accessed:
Revision history
- Initial English, Spanish and Japanese article prepared with automated assistance. The cited sources were checked for the complete article on 2026-10-29T03:09:31Z (UTC). Publication and preparation use the current date; no historical date was assigned. No independent clinical review is recorded.