eGFR – Understanding Kidney Function
The eGFR (estimated glomerular filtration rate) measures kidney function and indicates how well the kidneys filter the blood. A low value may indicate kidney disease.
Things worth knowing about "eGFR"
The eGFR (estimated glomerular filtration rate) measures kidney function and indicates how well the kidneys filter the blood. A low value may indicate kidney disease.
What is eGFR?
The eGFR, or estimated glomerular filtration rate, is the most important laboratory value for assessing kidney function. It indicates how much blood the kidneys are able to filter per minute and is expressed in ml/min/1.73 m² (millilitres per minute per 1.73 square metres of body surface area).
Because directly measuring the filtration rate is complex, the eGFR is calculated using blood markers – primarily creatinine – along with factors such as age, sex, and body size. The most widely used formulas are the CKD-EPI equation and the older MDRD formula.
What is eGFR Used For?
The eGFR is used primarily to diagnose and stage chronic kidney disease (CKD). It is also used to:
- monitor the progression of an existing kidney condition,
- assess cardiovascular risk,
- adjust the dosage of medications that are excreted by the kidneys,
- determine the right time to start renal replacement therapy (e.g., dialysis).
Normal Values and Interpretation
In healthy adults, the eGFR is typically above 90 ml/min/1.73 m². A gradual decline with age is considered physiologically normal. According to the KDIGO guidelines (Kidney Disease: Improving Global Outcomes), chronic kidney disease is classified into five stages based on eGFR:
- Stage G1: eGFR ≥ 90 – normal or high kidney function
- Stage G2: eGFR 60–89 – mildly decreased
- Stage G3a: eGFR 45–59 – mildly to moderately decreased
- Stage G3b: eGFR 30–44 – moderately to severely decreased
- Stage G4: eGFR 15–29 – severely decreased
- Stage G5: eGFR < 15 – kidney failure (end-stage renal disease)
Causes of a Low eGFR
A persistently low eGFR can have various causes, including:
- Diabetes mellitus – one of the most common causes of chronic kidney disease
- Arterial hypertension (high blood pressure) – damages the small blood vessels in the kidneys
- Glomerulonephritis – inflammation of the kidney filters
- Polycystic kidney disease – a genetic condition causing cysts in the kidneys
- Recurrent urinary tract infections or kidney stones
- Certain medications (e.g., non-steroidal anti-inflammatory drugs, some antibiotics)
Diagnosis and Measurement
The eGFR is calculated from a simple blood test. The level of creatinine – a waste product of muscle metabolism – is measured in the blood. Healthy kidneys filter creatinine efficiently; elevated levels suggest reduced filtration capacity.
In some cases, cystatin C is used as an additional marker, as it is less influenced by muscle mass and diet. The combined CKD-EPI formula using both creatinine and cystatin C is considered particularly accurate.
Treatment for Low eGFR
Treatment depends on the underlying cause and the stage of kidney disease:
- Blood pressure control: target values below 130/80 mmHg, often using ACE inhibitors or ARBs
- Blood glucose management in patients with diabetes
- Dietary adjustments: reduced protein, potassium, and phosphate intake depending on the stage
- Avoiding nephrotoxic substances (e.g., certain painkillers, contrast agents)
- Dialysis or kidney transplantation in end-stage renal failure (Stage G5)
References
- Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International, 2024.
- Levey AS et al. A new equation to estimate glomerular filtration rate. Annals of Internal Medicine, 2009; 150(9): 604–612.
- National Kidney Foundation. KDOQI Clinical Practice Guidelines for Chronic Kidney Disease: Evaluation, Classification, and Stratification. American Journal of Kidney Diseases, 2002.
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