A low result for your estimated Glomerular Filtration Rate (eGFR), calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula, indicates that your kidneys are not filtering waste from your blood effectively. This number is the best estimate of your remaining kidney function, measured in milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73m²). Health professionals use this value to assess kidney health and determine if you have chronic kidney disease (CKD). Understanding this result helps guide the next steps for monitoring and treatment.
Defining eGFR and the CKD-EPI Calculation
The Glomerular Filtration Rate (GFR) measures how efficiently the kidneys’ filtering units, called glomeruli, are cleaning the blood. These tiny structures remove waste products and excess fluid, and the GFR represents the total volume of blood cleaned per minute. Since directly measuring the GFR is a complex procedure, laboratories calculate the estimated GFR (eGFR) using a simple blood test.
The eGFR calculation relies on the level of creatinine in your blood, a waste product generated by muscle metabolism. Creatinine is produced at a relatively constant rate and is almost entirely removed by the kidneys. Therefore, its concentration serves as a proxy for filtration efficiency, where a higher level suggests a lower filtration rate.
The CKD-EPI equation uses your serum creatinine level, age, and sex to provide the eGFR value. This formula is the standard because it offers a precise estimate of kidney function compared to older methods. The 2021 CKD-EPI revision removed the race variable to promote equitable healthcare. By incorporating age and sex, the formula accounts for expected variations in muscle mass, which influences natural creatinine production.
Interpreting a Low eGFR Result
A normal eGFR result is typically 90 mL/min/1.73m² or higher, especially in young, healthy adults. Kidney function naturally declines with age, so a value in the 70s or 80s may still be considered normal if there are no other signs of kidney damage. Clinically, the term “low” applies when the eGFR falls below 60 mL/min/1.73m².
An eGFR below 60 mL/min/1.73m² is the main diagnostic threshold for Chronic Kidney Disease (CKD), regardless of whether other symptoms or signs of damage are present. To confirm a CKD diagnosis, this low eGFR must persist for three months or more. A single low reading might be caused by temporary issues, such as severe dehydration or certain medications. Therefore, repeat testing is required to establish chronicity.
Staging Reduced Kidney Function
Reduced kidney function severity is categorized using a system of GFR stages (G1 through G5). This classification system is used to determine the frequency of monitoring and the appropriate course of treatment.
Stage G1 (eGFR 90 or higher) is considered normal, but a CKD diagnosis requires evidence of kidney damage, such as protein in the urine. Stage G2 (eGFR 60–89) is a mild reduction and also requires evidence of kidney damage for a CKD diagnosis. The definitive diagnosis of CKD based solely on a low filtration rate begins at Stage G3.
GFR Stages
Stage G3 is separated into two subcategories: G3a (eGFR 45–59) and G3b (eGFR 30–44). Stage G4 is a severe reduction (eGFR 15–29), and this level often requires preparation for future kidney replacement therapy. The most advanced stage is G5 (eGFR below 15), which is classified as kidney failure.
Common Conditions that Lead to Lowered eGFR
A sustained low eGFR results from underlying systemic diseases that cause progressive damage to the kidney’s filtering structures over time. The two most frequent causes of chronic kidney disease globally are Type 2 Diabetes and high blood pressure (Hypertension). Uncontrolled high blood sugar from diabetes damages the small blood vessels within the kidneys, impairing filtration.
Persistently elevated blood pressure similarly strains the arteries supplying the kidneys, damaging the filtering units. Other conditions leading to reduced eGFR include:
- Autoimmune diseases, such as lupus.
- Inherited disorders like Polycystic Kidney Disease (PKD).
- Glomerulonephritis (inflammation of the glomeruli).
- Acute kidney injury (AKI), which can cause a sustained drop if the kidneys do not fully recover.
Monitoring and Management
Management for a low eGFR focuses on protecting remaining kidney function and slowing the rate of decline. Regular follow-up testing is necessary, with frequency determined by the CKD stage and underlying conditions. Patients with an eGFR below 60 mL/min/1.73m² require frequent monitoring of their kidney function and blood chemistries.
Controlling the underlying cause of kidney damage is the most effective strategy, including managing blood pressure and blood sugar levels. Medications such as Angiotensin-Converting Enzyme (ACE) inhibitors or Angiotensin Receptor Blockers (ARBs) are often prescribed to lower blood pressure and reduce protein leakage into the urine. Lifestyle changes are also integral to management, including adopting a kidney-friendly diet that may limit salt, potassium, and phosphorus intake as eGFR declines. Patients should avoid or use caution with nephrotoxic medications, such as Non-Steroidal Anti-Inflammatory Drugs (NSAIDs).