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Estimated Glomerular Filtration Rate (eGFR)

The estimated glomerular filtration rate (eGFR) is a blood test result that measures kidney function. It indicates how much blood the kidneys can filter per minute.

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Things worth knowing about "Estimated Glomerular Filtration Rate"

The estimated glomerular filtration rate (eGFR) is a blood test result that measures kidney function. It indicates how much blood the kidneys can filter per minute.

What Is the Estimated Glomerular Filtration Rate?

The estimated glomerular filtration rate (abbreviated eGFR) is a key laboratory value used to assess kidney function. It reflects how many milliliters of blood the kidneys are able to filter per minute. Because directly measuring this filtration capacity is complex, the eGFR is calculated using blood test results and established mathematical formulas -- hence the word estimated.

The eGFR is a cornerstone parameter in nephrology and is used to diagnose, stage, and monitor chronic kidney disease (CKD).

How Is the eGFR Calculated?

The eGFR is derived from the serum creatinine level combined with additional variables such as age and sex, and in some formulas, body size. Commonly used calculation methods include:

CKD-EPI equation (Chronic Kidney Disease Epidemiology Collaboration): Current gold standard, recommended for adults.
MDRD equation (Modification of Diet in Renal Disease): An older formula, now less widely used.
Schwartz equation: Specifically designed for children and adolescents.

Updated versions of the CKD-EPI formula (revised in 2021) no longer include race as a variable, promoting more equitable diagnostic standards.

Normal Values and Clinical Significance

The eGFR is expressed in units of ml/min/1.73 m², standardized to a reference body surface area. In healthy adults, an eGFR of 90 ml/min/1.73 m² or above is generally considered normal. It is important to note that eGFR naturally declines with age.

Based on eGFR values, CKD is classified into five stages:

Stage G1: eGFR ≥ 90 -- Normal or high filtration
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 below 15 -- Kidney failure, possibly requiring dialysis

Causes of a Reduced eGFR

A persistently low eGFR may indicate chronic kidney disease. Common underlying causes include:

Diabetes mellitus (diabetic nephropathy)
High blood pressure (hypertensive nephropathy)
Inflammatory kidney conditions (e.g., glomerulonephritis)
Polycystic kidney disease
Long-term use of certain medications (e.g., non-steroidal anti-inflammatory drugs)
Recurrent urinary tract infections

Symptoms of Reduced Kidney Function

A declining eGFR often causes no symptoms for a long time. As kidney function deteriorates further, the following signs may appear:

Fatigue and lack of energy
Fluid retention (edema), especially in the legs and face
Changes in urine volume or color
High blood pressure
Nausea and loss of appetite
Itchy skin

Diagnosis and Monitoring

The eGFR is determined through a routine blood test measuring the creatinine level, which is then entered into the appropriate formula. Additional tests often include urea, cystatin C, and a urine test for albumin (protein in the urine).

In patients with known kidney disease, the eGFR is monitored at regular intervals to track disease progression and guide treatment decisions.

Treatment for a Reduced eGFR

Management depends on the underlying cause and the stage of kidney disease. General approaches include:

Optimal control of blood pressure and blood sugar
A low-salt, protein-adjusted diet depending on the stage
Avoiding substances harmful to the kidneys
Medications such as ACE inhibitors or SGLT2 inhibitors
In advanced kidney failure: dialysis or kidney transplantation

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 -- Understanding Your Lab Values. www.kidney.org, accessed 2024.

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