An estimated Glomerular Filtration Rate (eGFR) is a measurement that assesses how well your kidneys are filtering waste from your blood. The eGFR test provides a picture of your kidney function, which is a fundamental aspect of overall health. This result is derived from a blood test and helps healthcare providers identify changes in kidney performance, sometimes before other signs of a problem appear.
Understanding Your eGFR Result
An eGFR result of 103 is considered to be in the normal, healthy range. For adults, an eGFR is typically above 90, which indicates that your kidneys are filtering waste from your blood effectively. Seeing a result like 103 suggests full kidney function.
The measurement for eGFR is expressed in units of mL/min/1.73m², which stands for milliliters per minute per 1.73 square meters of body surface area. This standardized unit allows for a consistent comparison of kidney function among different people. While an eGFR over 90 is normal, a result between 60 and 89 may be considered early-stage kidney disease if other signs of kidney damage are present, such as protein in the urine.
It’s also important to recognize that eGFR values are not static and can show some variability, as a single test provides a snapshot in time. For this reason, healthcare providers often look at trends in your eGFR over multiple tests to get a more complete understanding of your kidney health.
How eGFR is Calculated
The “e” in eGFR stands for “estimated” because the result is a calculated approximation, not a direct measurement. The calculation is derived from a blood test that measures creatinine, a waste product from the natural breakdown of muscle and digestion of protein. Healthy kidneys efficiently filter creatinine out of the blood.
To calculate your eGFR, laboratories use a formula that incorporates your serum creatinine level, age, and sex. When kidney function declines, less creatinine is filtered, causing its level in the blood to rise. The formula translates your creatinine level into an estimate of your filtration rate.
The medical community has updated the formulas used for this calculation, most notably by removing race as a variable. This adjustment improves the accuracy of the test and ensures the estimation of kidney function is more equitable across all populations. Race is a social construct, not a biological factor that determines creatinine levels.
Factors That Influence eGFR Levels
Several biological and lifestyle factors can influence your eGFR result. One of the most significant factors is age; eGFR naturally and gradually declines as a person gets older, even in individuals without kidney disease. This is a normal part of the aging process.
Hydration status at the time of the blood test can also cause temporary fluctuations. Being dehydrated can lead to a temporarily higher concentration of creatinine in the blood, which may result in a lower eGFR reading. Conversely, being well-hydrated can help ensure the result is an accurate reflection of your kidney function.
Diet and muscle mass play a role as well. Consuming a high-protein diet can increase creatinine production. Individuals with greater muscle mass may naturally have higher baseline creatinine levels, which could lead to a calculated eGFR that appears lower than their actual kidney function. Certain medications, including nonsteroidal anti-inflammatory drugs (NSAIDs) and some antibiotics, can also affect eGFR levels.
The Stages of Chronic Kidney Disease
The eGFR measurement is used by healthcare professionals to classify chronic kidney disease (CKD) into five distinct stages. This staging system helps to understand the progression of the disease and guide management. An eGFR result of 103 places you well within the normal range, indicating no evidence of CKD based on this value alone.
Stage 1 CKD is diagnosed when the eGFR is 90 or above, but there is other evidence of kidney damage, such as protein in the urine or physical damage to the kidneys. Stage 2 is characterized by an eGFR between 60 and 89 along with other signs of kidney damage. In these early stages, the kidneys are still functioning well, but monitoring is important.
The later stages reflect a more significant loss of kidney function. Stage 3 is defined by an eGFR between 30 and 59, and it is at this point that symptoms may begin to appear. Stage 4 involves an eGFR between 15 and 29, indicating severe loss of function. The final stage, Stage 5, is when the eGFR drops below 15, which is considered kidney failure.