eGFR: what it is, what it tells you and why we calculate it

eGFR is an estimate of how well your kidneys filter. It is not measured directly: it is calculated from the creatinine in your blood, taking age and sex into account. Together with urine albumin, it is the most common way to check your kidneys.

Why we calculate it

Your kidneys filter your blood all day and remove waste from it. eGFR shows how much they manage to filter.

They can slow down for years without symptoms. A falling eGFR shows it in time, while protecting them still makes a difference.

It matters for medicines and supplements too: if your kidneys filter less, some should be avoided or taken at lower doses. Your doctor decides.

What it tells you, and what it does not

If it is low, your kidneys may be filtering less. But it is an estimate: it comes from creatinine, which also depends on how much muscle you have.

One low result is not enough. Chronic kidney disease means a problem that lasts more than three months: an eGFR below 60, or another sign such as albumin in the urine.

And a normal eGFR does not tell the whole story: your kidneys can let albumin into the urine even while they filter well.

That is why it is read together with other tests:

• Creatinine: The number eGFR is calculated from
• Urine albumin: The earliest sign of kidney strain
• Potassium: It can rise when your kidneys filter less
• Glucose: Diabetes is a common cause of kidney damage

Normal eGFR levels

eGFR is expressed in mL/min/1.73 m². That is how many millilitres of plasma, the liquid part of your blood, your kidneys filter each minute, for a standard body size.

Your report may print only one limit, or none, because it is a calculation. Above 60, if your urine albumin is normal, your kidneys usually filter enough. Below 60 should always be seen by a doctor.

With age eGFR slowly falls, even in healthy people. That is why the same number reads differently when you are young and when you are old.

In the Rosa report you also see your optimal range, which takes your age into account.

What your result means

Find the row for your result, in mL/min/1.73 m². Which values should a doctor see? Anything below 60; below 45 soon, below 30 as soon as you can.

• Below 30: Much reduced. Your kidneys filter much less than normal. Talk to your doctor as soon as you can: they usually involve a nephrologist, a kidney specialist.
• 30 to under 45: Reduced. Your kidneys filter less. Sometimes a recent event, such as dehydration, is behind it. Talk to your doctor soon: they usually have the test repeated and look for the cause.
• 45 to under 60: Slightly reduced. Your kidneys filter a little less. Muscle, creatine or too little water can also play a part. Talk to your doctor, who usually has the test repeated together with urine albumin.
• 60 and above: Adequate. Your kidneys usually filter enough, if your urine albumin is normal. In the Rosa report you also see whether you are in your optimal range, for your age.

If your eGFR is low or high

• Low eGFR: Your kidneys may filter less, but muscle, creatine or too little water are sometimes behind it. Below 60 should be seen by a doctor.
• High eGFR: It is usually not a problem. With little muscle it can read higher than it is; if you have diabetes, show it to your doctor.

Low eGFR: why it falls

The first three usually do not mean kidney disease.

• Muscle and creatine: A lot of muscle or a creatine supplement raises creatinine, so the calculated eGFR falls. Your kidneys filter just as before.
• Too little water: If you are dehydrated, eGFR falls for a while. It comes back up once you drink normally again.
• Age: Over the years the kidneys filter a little less, even in healthy people.
• High blood pressure and diabetes: They are the most common causes of kidney damage. Over the years they can reduce how much your kidneys filter.
• Some medicines: Some lower only the estimate, others strain the kidneys, such as anti-inflammatories at high doses for a long time. Bring your doctor the list of what you take.
• Kidney diseases: Rarer: for example inflammation of the kidneys, or polycystic kidneys, an inherited disease. Your doctor assesses them.

eGFR and muscle: when it gets it wrong

eGFR comes from creatinine, a muscle waste product. The formula assumes average muscle for your age and sex.

If you have a lot of muscle, or take creatine, eGFR looks lower than it really is. If you have little, for example after a long illness or in very old age, it looks higher than it is.

When the doubt matters, your doctor can ask for another test, cystatin C, which does not depend on muscle. But an eGFR below 60 should still be seen by a doctor.

How to protect your kidneys

If your kidneys really filter less, there is no quick way to raise your eGFR. But you can protect them every day:

• Keep your blood pressure in check, and measure it now and then.
• If you have high glucose or diabetes, keep them in check with your doctor.
• Use little salt, do not smoke and move every day.
• Drink enough water, especially when it is hot or you exercise.
• Do not take anti-inflammatories such as ibuprofen for long periods without asking your doctor.

If your eGFR is below 60, your doctor decides on diet, medicines and supplements.

What can skew the result

A few things change the number for a while. It helps to know them before you read it.

• Creatine supplements: They raise creatinine and make eGFR look lower, even with healthy kidneys. Tell your doctor.
• Hard exercise: A tough workout in the days before can lower it for a short while. Arrive at the blood test rested.
• Too little water: If you are dehydrated, the number falls. You can drink water even while fasting.
• A meat meal: It can raise creatinine for many hours, so eGFR falls. Best to have the blood test fasting.

When to worry

Talk to your doctor if:

• Your eGFR is below 60: your doctor usually has the test repeated.
• It is below 45: talk to your doctor soon.
• It is below 30: talk to your doctor as soon as you can; they usually involve a nephrologist.
• Your report flags albumin in your urine, that is a urine albumin-to-creatinine ratio of 30 mg/g or more.
• It falls a lot from one test to the next.
• You pass much less urine than usual: see a doctor the same day.
• You pass almost no urine, or you are suddenly short of breath: call 112 or go to the emergency department.

With Rosa, an eGFR below 60 is always flagged to a doctor; below 45 and below 30 with more attention. The test is usually repeated to confirm it.

Frequently asked questions

What is a normal eGFR for my age? There is no single number: eGFR slowly falls with age, even in healthy people. Above 60, with normal urine albumin, your kidneys usually filter enough. In the Rosa report you see your optimal range, for your age.

Normal creatinine but low eGFR: how can that be? eGFR takes age and sex into account. Over the years the same creatinine means kidneys that filter less. So a creatinine within your report’s limits can give an eGFR below 60. If so, talk to your doctor, who usually has the test repeated.

What is the difference between GFR and eGFR? GFR is how much your kidneys really filter, but measuring it is complicated. eGFR estimates it from a simple blood test. Today it is used more often than clearance, which needs a 24-hour urine collection.

My report says CKD-EPI: what does it mean? It is the name of the formula used to calculate eGFR from creatinine. Some labs use others, such as MDRD: the results are similar, but not identical.

Is a high eGFR a problem? Usually not. With little muscle, though, it can read higher than it is. If you have diabetes, show it to your doctor: in the early years of diabetes the kidneys sometimes filter more than normal.

How often should it be checked? For people who feel well there is no fixed rule: Rosa calculates it twice a year, from the creatinine in each blood test. If it is below 60, it is usually checked again after about three months, or sooner if your doctor says so.

Sources

• KDIGO clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney International, 2024. PMID 38490803
• Inker and colleagues, new equations to estimate kidney filtration from creatinine and cystatin C. New England Journal of Medicine, 2021. PMID 34554658
• Delanaye and colleagues, kidney filtration falls with age: a definition of kidney disease that takes it into account. Journal of the American Society of Nephrology, 2019. PMID 31506289
• Groothof and colleagues, creatinine, cystatin C, muscle mass and mortality in two population cohorts. Journal of Cachexia, Sarcopenia and Muscle, 2024. PMID 38898741
• Tonneijck and colleagues, kidneys that filter too much in diabetes: causes, meaning and treatment. Journal of the American Society of Nephrology, 2017. PMID 28143897