Estimated Glomerular Filtration Rate

Estimated Glomerular Filtration Rate (eGFR) is one of the most important biomarkers for assessing kidney health and function. This calculated value estimates how efficiently your kidneys filter waste products and excess fluid from your blood, measured in milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73m²). The kidneys contain millions of tiny filtering units called glomeruli, which act like sophisticated sieves to remove toxins while retaining essential proteins and nutrients. eGFR provides a standardized way to evaluate this filtration capacity regardless of body size. Since kidney disease often progresses silently without symptoms until advanced stages, eGFR serves as an early warning system for declining kidney function. Regular monitoring of eGFR is particularly crucial for individuals with diabetes, hypertension, or cardiovascular disease, as these conditions significantly increase the risk of kidney damage. Understanding your eGFR empowers you to take proactive steps to protect your kidney health and overall wellbeing.

Kidney disease and declining eGFR often progress silently, earning chronic kidney disease the nickname "silent killer." Most people experience no symptoms until eGFR drops below 30 mL/min/1.73m², when kidney function is severely compromised. Early symptoms, when they occur, are often subtle and nonspecific, including fatigue, difficulty concentrating, poor appetite, and trouble sleeping. As eGFR continues to decline, more noticeable symptoms may develop, including swelling in ankles, feet, or hands due to fluid retention, shortness of breath, nausea and vomiting, muscle cramps, and persistent itching. Advanced kidney disease (eGFR below 15 mL/min/1.73m²) can cause severe symptoms including extreme fatigue, significant swelling, difficulty breathing, changes in urination patterns, metallic taste in mouth, and confusion. High blood pressure often accompanies declining kidney function and may be the only early sign. Conversely, temporarily elevated eGFR (hyperfiltration) typically causes no symptoms but may indicate underlying kidney stress from diabetes or hypertension. This is why regular testing is crucial, as symptoms appear too late to prevent significant kidney damage in most cases.

Optimizing eGFR focuses on protecting existing kidney function and addressing underlying risk factors. Blood pressure control is paramount, with target levels below 130/80 mmHg for most people and potentially lower for those with existing kidney disease. ACE inhibitors or ARBs are often preferred for their kidney-protective effects. Diabetes management through maintaining HbA1c below 7% significantly slows kidney function decline. Dietary modifications include limiting sodium to less than 2,300mg daily, moderating protein intake to 0.8-1.0 grams per kilogram of body weight for those with existing kidney disease, and maintaining adequate but not excessive hydration. The DASH diet pattern, emphasizing fruits, vegetables, whole grains, and lean proteins while limiting processed foods, supports kidney health. Regular exercise improves cardiovascular health and helps control blood pressure and blood sugar, indirectly protecting kidneys. Weight management reduces strain on kidneys and improves associated conditions. Smoking cessation is crucial, as smoking accelerates kidney function decline. Limit alcohol consumption and avoid NSAIDs when possible. Certain supplements like omega-3 fatty acids may provide modest kidney protection, but consult healthcare providers before starting any supplementation. Regular monitoring allows for early intervention when eGFR begins to decline, potentially slowing or stopping progression through timely treatment adjustments.

For optimal health and longevity, maintaining an eGFR above 90 mL/min/1.73m² is ideal, with values between 90-120 mL/min/1.73m² representing excellent kidney function. Research suggests that preserving kidney function within this optimal range is associated with reduced cardiovascular risk, better overall health outcomes, and increased longevity. Values consistently above 120-130 mL/min/1.73m² may indicate hyperfiltration, which can occur in diabetes, hypertension, or obesity and may predict future kidney decline if left unaddressed. From a longevity perspective, maintaining stable eGFR throughout life is more important than achieving maximum values. Studies show that even small declines in eGFR within the normal range can increase cardiovascular risk and mortality. The goal is to prevent the typical age-related decline through lifestyle optimization, aiming to maintain function as close to youthful levels as possible. Individuals with optimal kidney function should focus on prevention strategies to maintain their eGFR above 90 mL/min/1.73m² throughout their lifespan, as this range is associated with the lowest risk of kidney disease progression and cardiovascular complications.

Standard reference ranges for eGFR are categorized into stages that reflect kidney function status. An eGFR above 90 mL/min/1.73m² is considered normal kidney function, while values of 60-89 mL/min/1.73m² may indicate mild kidney disease or normal aging-related decline. An eGFR between 30-59 mL/min/1.73m² suggests moderate kidney disease, 15-29 mL/min/1.73m² indicates severe kidney disease, and below 15 mL/min/1.73m² represents kidney failure requiring dialysis or transplantation. Age significantly affects eGFR, as kidney function naturally declines by approximately 1 mL/min/1.73m² per year after age 30-40. Healthy young adults typically have eGFR values of 100-130 mL/min/1.73m², while values above 120 mL/min/1.73m² may sometimes indicate hyperfiltration, potentially signaling early kidney stress. Gender differences exist due to muscle mass variations, with men generally having slightly higher creatinine levels. Race-based adjustments in eGFR calculations have been debated and are being reevaluated by medical organizations to ensure accuracy across all populations.

eGFR measures the volume of blood that your kidneys can filter per minute, adjusted for standard body surface area. This biomarker is calculated using mathematical formulas that incorporate your serum creatinine level, age, sex, and race. Creatinine is a waste product produced by muscle metabolism that healthy kidneys should efficiently remove from the bloodstream. When kidney function declines, creatinine accumulates in the blood, leading to a lower calculated eGFR. The measurement reflects the overall filtering capacity of both kidneys combined and provides insight into how well they're performing their essential functions of waste removal, fluid balance, and blood pressure regulation. Unlike direct measurement of kidney function, which would require complex procedures, eGFR offers a practical and reliable estimate that correlates well with actual glomerular filtration rate. This makes it an invaluable tool for detecting chronic kidney disease in its early stages, monitoring disease progression, and guiding treatment decisions to preserve remaining kidney function.

Multiple factors can influence eGFR levels, both temporarily and permanently. Chronic conditions like diabetes and hypertension are the leading causes of kidney damage, gradually reducing eGFR over time through different mechanisms. Diabetes causes damage through high blood sugar levels, while hypertension damages kidney blood vessels through excessive pressure. Cardiovascular disease, autoimmune disorders, and genetic kidney diseases also contribute to declining function. Medications can significantly impact eGFR, including NSAIDs (ibuprofen, naproxen), certain antibiotics, contrast dyes used in imaging, and ACE inhibitors, though the latter may cause temporary decreases while providing long-term kidney protection. Dehydration can temporarily lower eGFR by reducing blood flow to the kidneys, while overhydration might temporarily increase it. Diet plays a crucial role, with high protein intake potentially increasing eGFR acutely but potentially stressing kidneys long-term. Excessive sodium intake contributes to hypertension and kidney damage. Lifestyle factors like smoking, excessive alcohol consumption, and obesity negatively affect kidney function. Age is an unavoidable factor, with natural decline beginning around age 30. Intense exercise can temporarily affect eGFR, so testing should be avoided immediately after strenuous activity.

eGFR testing should be performed annually for healthy adults over 40, and more frequently for those with risk factors. Individuals with diabetes, hypertension, cardiovascular disease, family history of kidney disease, or obesity should be tested every 6-12 months. eGFR is typically included in comprehensive metabolic panels (CMP) or basic metabolic panels (BMP) and requires only a simple blood draw. Testing should be done in a fasting state when possible, and patients should avoid intense exercise 24 hours before testing, as it can temporarily affect results. For accurate results, maintain consistent hydration and avoid excessive protein intake the day before testing. eGFR testing is usually combined with urinalysis and urine albumin testing, as these provide complementary information about kidney health. Two abnormal eGFR results at least 90 days apart are typically required to diagnose chronic kidney disease. Individuals taking medications that affect kidney function may need more frequent monitoring, as determined by their healthcare provider.