Estimated Creatinine Clearance (eGFR) is a measurement used to assess kidney health. It helps healthcare providers detect potential kidney issues early and monitor kidney function over time.
Understanding Creatinine and Its Clearance
Creatinine is a waste product generated from the normal breakdown of muscle tissue and the digestion of protein in food. It originates from creatine, a compound stored in muscles that supplies energy. The body produces creatinine at a relatively constant rate, largely proportional to an individual’s muscle mass.
The kidneys are responsible for filtering waste products, including creatinine, from the blood; this process is known as clearance. Healthy kidneys efficiently remove creatinine from the bloodstream, excreting it through urine. If kidney function declines, the kidneys become less effective at clearing creatinine, leading to an increased concentration in the blood, which indicates impaired filtration.
The “Estimated” Process: How eGFR is Calculated
Directly measuring the glomerular filtration rate (GFR), the precise rate at which kidneys filter blood, is complex, time-consuming, and often invasive. For routine clinical practice, an estimated GFR (eGFR) is used instead, providing a practical and accessible proxy for kidney function. This estimation relies on formulas that incorporate various factors, primarily the level of creatinine in the blood, along with a person’s age and sex.
Historically, some eGFR formulas included race, specifically for Black individuals, based on observations of potentially higher muscle mass and thus higher creatinine levels. However, using race in these calculations could lead to an overestimation of kidney function in some Black patients, potentially delaying diagnosis or access to necessary care.
Consequently, major medical organizations, including the National Kidney Foundation and the American Society of Nephrology, have recommended removing race from eGFR calculations. Newer, race-free equations, such as updated versions of the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation, are now the recommended standard for estimating GFR.
Why Creatinine Clearance is Measured
eGFR plays a central role in assessing kidney function and detecting kidney disease. It allows healthcare providers to identify kidney problems early, often before symptoms appear. Early detection is important because kidney disease can progress silently, and timely intervention can help manage the condition.
eGFR is also used to classify the stages of Chronic Kidney Disease (CKD), which helps monitor disease progression. Staging allows for tailored management plans and helps predict potential outcomes.
Furthermore, eGFR results are important for guiding medication dosages. Many medications are cleared from the body by the kidneys, and their dosages may need adjustment based on kidney function to prevent drug accumulation and potential toxicity.
Interpreting Your Results and Influencing Factors
For adults, an eGFR of 90 milliliters per minute per 1.73 square meters (mL/min/1.73m²) or higher is generally considered within the normal range. However, eGFR naturally declines with age, even in individuals without kidney disease. If an eGFR consistently falls below 60 mL/min/1.73m² for three months or longer, it typically indicates chronic kidney disease. Lower eGFR values correspond to more advanced stages of kidney disease, with values below 15 mL/min/1.73m² indicating kidney failure.
Several factors can influence or temporarily alter creatinine levels and, consequently, eGFR results. Muscle mass is a significant factor; individuals with higher muscle mass, such as bodybuilders or some males, tend to have higher creatinine levels, which can make their eGFR appear lower than their actual kidney function. Conversely, those with lower muscle mass, including females, the elderly, individuals with muscle wasting conditions, or those on vegetarian diets, may have lower creatinine levels, potentially leading to an overestimation of their eGFR.
Dietary intake, particularly a high meat diet, can temporarily increase creatinine levels, while vegan or vegetarian diets may result in lower levels. Certain medications, such as some antibiotics, anti-inflammatory drugs, or stomach acid reducers, can also affect creatinine levels or kidney function. Dehydration, pregnancy, or severe liver disease can also temporarily influence creatinine levels. Given these variables, a healthcare professional is best equipped to interpret eGFR results in the context of an individual’s overall health and medical history.