Estimated Glomerular Filtration Rate (eGFR) provides insight into kidney function. It represents the rate at which the kidneys filter waste products from the blood. The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is the most commonly used method for calculating eGFR, offering a standardized approach to assessing kidney health for individuals. This calculation is a fundamental tool for healthcare professionals to identify and monitor kidney conditions.
Understanding Estimated Glomerular Filtration Rate (eGFR)
Kidneys contain millions of tiny filtering units called glomeruli, which are responsible for removing waste and excess water from the bloodstream to produce urine. A healthy GFR means these filters are working efficiently to keep the body’s internal environment balanced.
Measuring GFR directly is a complex and time-consuming procedure, making it impractical for routine clinical use. Instead, an estimated GFR (eGFR) is calculated using a formula that incorporates the level of creatinine in the blood. Creatinine is a waste product generated from the normal breakdown of muscle tissue. When kidney function declines, creatinine can build up in the blood, indicating reduced filtration.
A lower eGFR suggests that the kidneys are not filtering as well as they should, which can be an early sign of kidney problems. While a normal eGFR is typically above 90 milliliters per minute per 1.73 square meters (mL/min/1.73m²), it is important to remember that eGFR naturally decreases with age, even in individuals without kidney disease.
The CKD-EPI Equation: A Key Measurement
The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation was developed to provide a more accurate assessment of kidney function compared to older formulas, such as the Modification of Diet in Renal Disease (MDRD) equation. Its improved accuracy is particularly notable at higher GFR values, which helps in identifying kidney disease more precisely across a broader range of kidney function.
The CKD-EPI equation calculates eGFR by considering several patient-specific factors, including serum creatinine levels, age, and sex. The latest version of the CKD-EPI equation, updated in 2021, notably removed the race coefficient, which was previously included in earlier versions.
This change was implemented to provide a more equitable estimate of GFR across diverse populations, addressing concerns that the previous inclusion of race could overestimate GFR in certain groups. The CKD-EPI equation’s widespread use and continuous refinement underscore its importance as a reliable tool for kidney disease screening and diagnosis. While the detailed mathematical formula is complex, healthcare providers utilize automated systems to apply these factors and determine the eGFR.
Interpreting Your eGFR Results and Next Steps
Healthcare providers use eGFR values to classify the stages of Chronic Kidney Disease (CKD). Generally, an eGFR below 60 mL/min/1.73m² for three months or more, or an eGFR above 60 with signs of kidney damage (like protein in urine), indicates CKD.
The stages of CKD are categorized based on eGFR values:
Stage 1: eGFR of 90 or higher, often with signs of kidney damage (e.g., protein in urine).
Stage 2: eGFR of 60 to 89, also with evidence of kidney damage.
Stage 3a: eGFR between 45 and 59.
Stage 3b: eGFR between 30 and 44.
Stage 4: eGFR between 15 and 29 (severe reduction).
Stage 5: eGFR below 15 (kidney failure).
If your eGFR results suggest kidney impairment, your healthcare provider will likely recommend regular monitoring, which may include repeat eGFR tests and urine tests, such as the urine albumin-creatinine ratio (uACR), to check for protein in the urine. These tests help to track the progression of kidney disease and guide treatment decisions. Lifestyle adjustments are a primary recommendation to help manage kidney health.
Maintaining a healthy lifestyle includes adopting a balanced diet, which often means reducing sodium intake and focusing on fresh fruits, vegetables, and whole grains. Regular physical activity also contributes to kidney health by helping to manage blood pressure and blood sugar levels. It is also beneficial to avoid smoking and limit alcohol consumption, as these can negatively impact kidney function. If you have conditions like diabetes or high blood pressure, managing them effectively with your doctor’s guidance is important for protecting your kidneys. Consulting with your doctor or a nephrologist is important for personalized advice and management of your kidney health.