What Is eGFR, and What Does a Low Result Mean?
A doctor explains what eGFR measures, what the chronic kidney disease stages mean, and why one low result is not the same as kidney disease.
The short version
- eGFR estimates how much blood your kidneys filter each minute, calculated from a blood creatinine level along with your age and sex.
- Above 90 is normal, 60 to 89 is mildly reduced and often normal for age, and below 60 sustained for three months defines chronic kidney disease.
- One low reading is not a diagnosis - dehydration, a high-protein meal, heavy exercise and some medicines all lower it temporarily.
See a doctor promptly if
These are the signs that change this from something to read about into something to act on.
- Passing much less urine than usual, or none at all
- A sharp fall in eGFR over days to weeks rather than years
- Visible blood in the urine, or heavy frothy urine with swollen ankles and face
- Breathlessness with swelling and a known low eGFR
eGFR stands for estimated glomerular filtration rate, and it estimates how many milliliters of blood your kidneys filter every minute. It is calculated, not measured directly, from your blood creatinine level together with your age and sex. A low eGFR means the kidneys are filtering more slowly than expected, which may reflect genuine damage, or may simply reflect the day you had the test.
That distinction is the whole point. One low reading is not chronic kidney disease.
What the numbers mean#
| eGFR (mL/min/1.73m2) | Stage |
|---|---|
| 90 or above | Normal filtration |
| 60 to 89 | Mildly reduced - often normal for age |
| 45 to 59 | Stage 3a |
| 30 to 44 | Stage 3b |
| 15 to 29 | Stage 4 |
| Below 15 | Stage 5, kidney failure |
Chronic kidney disease is defined as an eGFR below 60 that has persisted for at least three months, or evidence of kidney damage such as protein in the urine even when eGFR is normal.
Why the urine test matters as much as the blood test#
The single most useful companion test is the urine albumin to creatinine ratio, or ACR. Protein leaking into the urine indicates damage to the filters themselves, and it predicts progression and cardiovascular risk better than eGFR alone. An eGFR of 70 with significant protein in the urine is more concerning than an eGFR of 62 with none. If you have only had the blood test, the urine test is a reasonable thing to ask about.
Why a single result can be misleading#
Creatinine comes from muscle. More muscle means higher creatinine and therefore a lower calculated eGFR, which is why very muscular people are sometimes flagged incorrectly. Very low muscle mass does the opposite and can hide real impairment.
Dehydration lowers eGFR temporarily, as does a large meat meal a few hours before the test, intense exercise the day before, and some medicines. Certain drugs, including trimethoprim and some diabetes medicines, raise creatinine by blocking its secretion without affecting actual filtration.
What protects kidney function#
The two dominant causes of chronic kidney disease globally are diabetes and high blood pressure, and controlling both is the most effective protection there is. Blood pressure control has the strongest evidence of anything on the list.
Beyond that: avoid regular use of anti-inflammatory painkillers such as ibuprofen if your eGFR is already reduced, stay well hydrated in hot work environments, stop smoking, and tell any prescriber your eGFR so doses can be adjusted. During illness with vomiting or diarrhea, some medicines are temporarily paused; ask your own doctor which of yours are on that list.
The wider picture#
Kidney numbers rarely stand alone on a report, and the fuller guide to understanding your blood test results explains how eGFR sits alongside the other markers on the same page.
Common questions
Is eGFR of 60 to 89 kidney disease?
Why does my eGFR change between tests?
Does high protein intake damage kidneys?
Sources
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