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eGFR briefly explained
eGFR is a laboratory value used to estimate how well the kidneys filter the blood. The higher the eGFR, the better the kidneys' purification ability works.
The value is calculated based on substances in the blood that are normally filtered out by the kidneys, mainly creatinine and Cystatin C. Since kidney function cannot be measured directly, eGFR is used as an indirect but reliable measure.
An eGFR below 60 mL/min/1.73 m² for a long time may indicate chronic kidney disease, but a single deviation does not necessarily mean that the kidneys are diseased. eGFR can vary temporarily, for example in the event of dehydration or infection.
In the event of repeated low values, rapid deterioration or if you have symptoms or known risk factors, eGFR should always be followed up by healthcare.
Have you received an eGFR value in your test results and are wondering what it really says about your kidney function? You are far from alone. eGFR is used daily in healthcare but is rarely explained in an understandable way.
Kidneys are vital organs that work silently in the background, 24/7. They purify the blood of waste products, regulate fluid balance and salt content, and contribute to hormone production that affects blood pressure and blood formation.
A laboratory value called eGFR is often used to assess how well the kidneys are functioning. Despite eGFR being a central measurement in healthcare, many people have never received a clear explanation of what the value actually means.
What does eGFR mean?
eGFR stands for estimated glomerular filtration rate. Simply put, eGFR describes how quickly the kidneys filter the blood and clear away waste products. The higher the eGFR, the better the kidneys' filtration ability. A low eGFR may indicate that the kidneys are not working properly.
That is why eGFR is calculated instead of measuring kidney function directly
Unlike many other organs, the kidneys' filtration ability cannot be measured directly with a regular blood test. Instead, kidney function must be estimated indirectly – by analyzing how well the kidneys manage to clean the blood of certain substances.
When kidney function deteriorates, these substances begin to accumulate in the blood. By measuring their concentration and using mathematical calculations, a reliable estimate of how effective the kidneys' filtration is can be obtained.
The most common calculations of eGFR are based on creatinine and Cystatin C – two substances that are normally filtered out by the kidneys and therefore provide important information about kidney function.
The difference between relative and absolute eGFR
Most eGFR values reported are relative, meaning that the result is normalized to a standard body surface area of 1.73 m². This makes it possible to compare kidney function between different people.
Absolute eGFR instead takes into account the individual's actual body size through weight and height and is mainly used in special contexts, such as when dosing drugs.
How eGFR is used in healthcare
eGFR is one of the most important laboratory values for assessing kidney function and is used daily in both primary care and specialist care. The value serves as a common language to describe how well the kidneys are doing their job of cleaning.
In healthcare, eGFR is used, among other things, to:
- detect early kidney disease before symptoms have occurred.
- assess how severely kidney function is impaired.
- monitor changes in kidney function over time.
- adjust drug dosage and avoid side effects.
Kidney disease often develops slowly and rarely causes clear symptoms in the early stages. Therefore, a lowered eGFR can be one of the first signs that the kidneys are affected, even in people who otherwise feel healthy.
What does a low eGFR mean?
An eGFR below 60 mL/min/1.73 m² for a long time may indicate chronic kidney disease. The lower the eGFR, the more impaired the kidney function. However, it is important to interpret the eGFR in context. Age, other diseases, medications and temporary factors such as dehydration or infection can affect the value.
eGFR can vary from time to time, especially during temporary stress on the body and with lower fluid intake. A single deviation therefore does not always mean that the kidneys are diseased.
When should I contact healthcare?
A single deviating eGFR value does not necessarily mean that the kidneys are diseased, especially if you are otherwise well. However, a clearly lowered or decreasing eGFR should always be followed up. Contact healthcare or your treating physician for further assessment if:
- eGFR repeatedly falls below 60 mL/min/1.73 m².
- eGFR drops rapidly between different tests.
- you also have symptoms such as fatigue, swelling, decreased urine output or high blood pressure.
- you have known kidney disease, diabetes, high blood pressure or cardiovascular disease.
In the event of significantly different values or suspicion of acute kidney damage, healthcare should always be contacted urgently.