What Does a Low eGFR Mean on a Blood Test?
A low eGFR on a blood test can mean your estimated kidney filtration is below 60 mL/min/1.73 m² or has fallen from your baseline. A persistent eGFR below 60 is a common CKD threshold, and one low reading can be temporary.
A low eGFR on a blood test can mean an estimated glomerular filtration rate below 60 mL/min/1.73 m² or a meaningful fall from your baseline. A persistent eGFR below 60 is a common CKD threshold, while eGFR 60-89 can still matter if there is albuminuria, blood in urine, an imaging abnormality, or other evidence of kidney damage. It is not a direct measurement of kidney damage, and one low reading can be temporary.
What does a low eGFR mean on a blood test?
Your kidneys contain roughly two million glomeruli, small filters that move waste out of blood. A routine blood test cannot measure each filter's work directly, so labs commonly measure creatinine, a waste product left behind by muscle turnover, and run it through the CKD-EPI 2021 equation with your age and sex. Higher creatinine generally means less filtering is happening. The output is the eGFR, in millilitres per minute per 1.73 m² of body surface area. A low eGFR means the model estimates filtration below 60 mL/min/1.73 m² or a meaningful drop from your previous level.
A single low eGFR is a signal, not a diagnosis. Repeat it before you believe it.
Why creatinine can fool the estimate
Creatinine is a decent marker, but it is not kidney-specific. Its blood level depends on how much muscle you carry, how hydrated you are, and what you did before the draw. A low eGFR can appear without kidney disease in several situations:
- Dehydration from illness, heat, fasting, or not drinking enough before the test.
- A heavy workout in the 24 to 48 hours before the draw.
- Creatine supplements, which can raise creatinine without damaging the kidneys.
- Large muscle mass, which creates more creatinine at baseline.
- Some medicines, such as trimethoprim, that can raise creatinine without reducing true filtration.
The opposite error happens too. Low muscle mass from ageing, illness or very low body weight can keep creatinine low, so eGFR looks better than true kidney function. This is why a creatinine-based eGFR is a starting point, not a verdict.
How to read your own lab report
Find the line that says eGFR, estimated GFR or estimated glomerular filtration rate. It will usually be reported in mL/min/1.73 m². Many labs calculate eGFR from creatinine, age and sex, but some use cystatin C or other methods. If your lab did not calculate it, you can estimate it yourself with creatinine, age and sex and the CKD-EPI 2021 equation. You do not need your weight or a urine sample for the basic creatinine-based eGFR.
Use the units and sex option shown on the HealthOS calculator page. If the lab report is unclear, ask a clinician rather than guessing which unit or sex input applies. Many lab reports group eGFR results above 60. If your report says greater than 60, do not over-interpret a calculated number like 87 or 92; a value above 60 should not be over-interpreted.
Then read the number in stages.
| eGFR result | Stage | What it usually means |
|---|---|---|
| 90 or above | G1 | Normal or high filtration; kidney disease can still exist if urine has albumin. |
| 60 to 89 | G2 | Mildly reduced; can still matter with albuminuria, blood in urine, or imaging abnormality. |
| 45 to 59 | G3a | Mild to moderate reduction; doctors usually recheck and check urine. |
| 30 to 44 | G3b | Moderate reduction; usually needs monitoring. |
| 15 to 29 | G4 | Severe reduction; usually needs specialist involvement. |
| Below 15 | G5 | Kidney failure range; treatment decisions depend on symptoms and labs. |
Scroll the table sideways for the rest →
Based on standard CKD staging. A single eGFR result is not enough to diagnose CKD; urine albumin and repeated tests are part of staging.
The number that often changes decisions is 60, but CKD assessment is not based on eGFR alone. A persistent eGFR below 60 for three months or more is a common line for chronic kidney disease in adults. Guidelines assess CKD with repeated eGFR and urine albumin testing, not one blood number. A single result just below 60, especially after dehydration or a hard workout, is not the same thing. Values from 60 to 89 can still matter if there is albuminuria, blood in urine, an imaging abnormality, or other evidence of kidney damage.
When the number is just under 60
This is the most common follow-up question. A 58 or 59 can mean early kidney disease, or it can mean you were dry and your muscles were recovering. Doctors usually recheck before calling it chronic. In older adults, eGFR tends to decline with age, so the trend should be interpreted with a clinician. A stable 55 in a 75-year-old is different from a dropping 55 in a 35-year-old. The trend matters more than one value.
If the repeat is still low, the obvious next test is a urine albumin-to-creatinine ratio, called uACR. Kidney disease is staged by eGFR and albuminuria together. Many people fixate on the blood number and ignore urine protein, but the urine result is often the stronger risk signal.
When a low eGFR is worth taking to a doctor
Take the result to a doctor if:
- eGFR is below 60 on two tests at least three months apart.
- Your eGFR is falling steadily or has dropped across a CKD stage.
- You also see protein or blood in your urine, swelling, high blood pressure, nausea, or you are passing less urine.
- You have diabetes, high blood pressure, or a family history of kidney disease and the number is below 90.
- Your eGFR is 60 to 89 and you have albuminuria, blood in urine, or an imaging abnormality.
A one-off low number with no other signs is usually rechecked before anything else. A low number plus symptoms is more urgent.
Run your own lab numbers through the free eGFR calculator. It uses the CKD-EPI 2021 creatinine equation with no race term, is free, runs in your browser, and is not a diagnosis. HealthOS results are for information only, not medical advice, and may be inaccurate.
Written by
HealthOS Research