The estimated glomerular filtration rate (eGFR) is a crucial measure used to assess how well the kidneys are functioning. It estimates the rate at which the kidneys filter waste and excess fluids from the blood, helping to evaluate overall kidney health. A decrease in the eGFR value can be an early indicator of kidney disease, allowing for timely intervention and management.
What is eGFR?
The glomerular filtration rate (GFR) is a test that measures the rate at which blood is filtered through the kidneys. GFR is essential for determining how well the kidneys are performing their role in filtering out toxins, excess waste, and fluids from the bloodstream.
The estimated glomerular filtration rate (eGFR) is a calculated value based on a blood test that measures the level of serum creatinine in the blood, along with other factors like age, sex, and ethnicity. Creatinine is a waste product produced by muscles, and its levels in the blood can give an estimate of kidney function.
While the GFR test is usually performed in a medical setting through blood work, the eGFR is a more commonly used estimate, derived from serum creatinine levels, which can be calculated using various equations.
How eGFR is Calculated
The eGFR is calculated using the Modification of Diet in Renal Disease (MDRD) study equation or the more commonly used Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. Both formulas take into account the serum creatinine levels, along with other factors such as:
- Age
- Sex
- Race/ethnicity (because kidney function can vary across different populations)
For example, the eGFR formula might look like this: eGFR=141×(SerumCreatinine0.9)−0.411×(Age40)−0.302×(1.159 if female)×(1.16 if African American)eGFR = 141 \times \left(\frac{Serum Creatinine}{0.9}\right)^{−0.411} \times \left(\frac{Age}{40}\right)^{−0.302} \times (1.159 \text{ if female}) \times (1.16 \text{ if African American})eGFR=141×(0.9SerumCreatinine)−0.411×(40Age)−0.302×(1.159 if female)×(1.16 if African American)
Different labs may use slightly modified equations or constants, but the goal is to produce an estimate of kidney function, usually expressed in milliliters per minute per 1.73 m² (mL/min/1.73m²), which is standardized for an average adult body surface area.
Why is eGFR Important?
The eGFR is an essential diagnostic tool for assessing kidney function and for the early detection of chronic kidney disease (CKD). The kidneys filter waste products and excess fluid from the bloodstream, and a decrease in eGFR may signal that the kidneys are not working effectively.
1. Identifying Kidney Disease Early
- A lower eGFR can indicate early-stage kidney disease, even before any noticeable symptoms occur. By identifying kidney dysfunction early, doctors can implement strategies to slow the progression of kidney disease, such as controlling blood pressure, managing diabetes, or avoiding nephrotoxic medications.
2. Monitoring Kidney Function
- For individuals diagnosed with kidney disease or those at high risk (such as those with diabetes, hypertension, or a family history of kidney disease), monitoring eGFR is important for tracking kidney function over time. Regular eGFR tests can help healthcare providers assess how well kidney disease is being managed.
3. Guide for Treatment Decisions
- An eGFR test can guide medical treatment decisions. If a person has low eGFR values, it may indicate the need for more intensive treatments, including dialysis or a kidney transplant for those with end-stage kidney disease (ESKD).
What Do eGFR Results Mean?
eGFR results are typically classified into different stages, depending on the value of the eGFR. The normal range for eGFR is generally considered to be 90 mL/min/1.73m² or higher in healthy adults.
eGFR Stages of Chronic Kidney Disease (CKD)
- Stage 1 (Normal or High Function)
- eGFR ≥ 90 mL/min/1.73m²
- Normal kidney function, but there may be signs of kidney damage, such as protein in the urine or structural abnormalities in the kidneys.
- Stage 2 (Mildly Decreased Function)
- eGFR 60-89 mL/min/1.73m²
- Mild decrease in kidney function. Kidney damage may still be present, but the kidneys are functioning well overall.
- Stage 3 (Moderate Decrease in Kidney Function)
- eGFR 30-59 mL/min/1.73m²
- Moderate decrease in kidney function. This stage is further divided into Stage 3a (eGFR 45-59) and Stage 3b (eGFR 30-44).
- Symptoms of kidney disease may begin to appear, such as fluid retention, high blood pressure, and changes in urination.
- Stage 4 (Severe Decrease in Kidney Function)
- eGFR 15-29 mL/min/1.73m²
- Severe decline in kidney function. At this stage, kidney disease is more advanced, and patients may experience significant symptoms.
- Stage 5 (End-Stage Kidney Disease, ESKD)
- eGFR < 15 mL/min/1.73m²
- End-stage kidney disease or kidney failure. Kidney function is severely compromised, and dialysis or a kidney transplant is typically required.
Factors That Can Affect eGFR Results
While eGFR is a useful tool, it can be influenced by several factors:
1. Age
- Kidney function naturally declines with age. Older individuals may have lower eGFR values, even if they have no kidney disease.
2. Gender
- Women generally have lower muscle mass compared to men, which results in lower creatinine levels. Consequently, women may have a slightly lower eGFR than men, even if kidney function is similar.
3. Race/Ethnicity
- Different equations may be used to adjust eGFR results for race, as studies have shown that African Americans tend to have higher muscle mass and higher serum creatinine levels, which can influence eGFR calculations.
4. Muscle Mass
- Since serum creatinine is produced by muscle breakdown, individuals with higher muscle mass (like athletes) may have higher creatinine levels, which could result in a falsely low eGFR.
5. Medications
- Certain medications, such as those that affect kidney function or affect the metabolism of creatinine, can influence eGFR results. For instance, ACE inhibitors or ARBs may alter kidney function, impacting eGFR.
6. Acute Illness or Injury
- In cases of dehydration, acute kidney injury (AKI), or severe infections, eGFR values may temporarily drop, even in individuals without chronic kidney disease.
How to Improve Kidney Health Based on eGFR Results
If your eGFR results indicate early-stage kidney disease, there are several steps you can take to help preserve kidney function:
1. Control Blood Pressure
- High blood pressure is a major cause of kidney damage. Aim for a target blood pressure of 130/80 mm Hg or lower, especially if you have kidney disease.
2. Manage Blood Sugar Levels
- Diabetes is another leading cause of kidney disease. Maintaining blood sugar levels within the target range can help prevent or slow the progression of kidney damage.
3. Limit Protein Intake
- If you have kidney disease, reducing protein intake can reduce the kidneys’ workload. This is especially important in the later stages of kidney disease.
4. Avoid Nephrotoxic Medications
- Certain medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), can damage the kidneys. Avoid overusing these drugs and consult with your healthcare provider about alternatives.
5. Stay Hydrated
- Proper hydration helps the kidneys filter waste efficiently. However, in advanced kidney disease, fluid intake may need to be monitored to avoid fluid overload.
6. Regular Monitoring
- Regular eGFR testing is crucial for individuals with risk factors for kidney disease, such as diabetes, hypertension, or a family history of kidney disease.
Conclusion
The estimated glomerular filtration rate (eGFR) is an essential tool in diagnosing and monitoring kidney function. It provides important information about how well the kidneys are filtering blood and helps doctors assess the risk of kidney disease. By understanding your eGFR results, you can take proactive steps to protect your kidney health and prevent further damage. Regular check-ups and lifestyle changes, such as controlling blood pressure, managing diabetes, and avoiding kidney-damaging substances, can help preserve kidney function and improve overall health.