Navigating medical test results can often feel overwhelming, especially when the terminology is unfamiliar. The Estimated Glomerular Filtration Rate (eGFR) is a calculation derived from a simple blood test that offers a snapshot of how effectively your kidneys are working. These two organs perform the continuous task of filtering waste products and excess fluid from your blood to maintain balance within the body. Understanding your eGFR result is a direct way to assess your kidney health and identify any potential need for monitoring or intervention.
Understanding the eGFR Test
The eGFR is an estimate of the Glomerular Filtration Rate (GFR), which is considered the standard measure of kidney function. The kidneys contain millions of tiny filtering units called glomeruli that clean the blood. The GFR represents the volume of blood these glomeruli can effectively clean over a specific period, reflecting the overall efficiency of the organs.
Because directly measuring the actual GFR is complex and time-consuming, laboratories calculate the eGFR using a mathematical formula. This calculation primarily relies on the level of creatinine found in your blood. Creatinine is a common waste product produced by the breakdown of muscle tissue, which healthy kidneys filter out and excrete through urine.
The resulting eGFR number is reported in milliliters per minute per 1.73 meters squared (mL/min/1.73m²), adjusting the result for an average body surface area. A higher eGFR value indicates better kidney function, meaning a greater volume of blood is being filtered efficiently. This number provides clinicians with a consistent way to screen for kidney problems and monitor the progression of any existing condition.
Interpreting an eGFR of 104
An eGFR result of 104 is considered an excellent finding that signifies healthy, optimal kidney function. For adults, an eGFR reading of 90 or above falls within the normal range, indicating the kidneys are working at a high level of performance. A score of 104 is well above the threshold that would raise concern for impairment.
Doctors assess kidney health using a five-stage system for Chronic Kidney Disease (CKD), primarily based on the eGFR value. CKD Stage 1 is defined as having an eGFR of 90 or greater, but only if there is accompanying evidence of kidney damage. In the absence of other damage markers, an eGFR of 104 is classified as normal function.
A key marker checked alongside the eGFR is the presence of albumin, a protein, in the urine (albuminuria). If a person has an eGFR of 104 but also shows high levels of albuminuria, they are classified as having Stage 1 CKD. This means the kidneys are still working well but are showing signs of mild damage. For most people, however, a result this high confirms that the kidneys are performing their vital filtration role and indicates a robust filtration capacity, often seen in younger, healthy adults.
Factors Influencing eGFR Results
The eGFR calculation is an estimate, and its accuracy is influenced by several biological and demographic factors beyond the serum creatinine level. Standard formulas, such as the CKD-EPI equation, incorporate demographic variables like age and sex to adjust the final result. This adjustment recognizes that creatinine production naturally varies between individuals based on these characteristics.
Muscle Mass
A person with larger muscle mass naturally has more creatinine in their blood, which can lead to a falsely low eGFR estimate. Creatinine is a muscle waste product, and the equation assumes an average amount of muscle for a person’s age and sex. Conversely, individuals with very low muscle mass may have an eGFR that appears higher than their actual kidney function.
Transient Factors
Other transient factors can temporarily skew the result, which is why a single test may not tell the whole story. Acute dehydration can concentrate the blood, leading to a temporary change in creatinine levels that affects the eGFR calculation. Similarly, consuming large amounts of cooked meat or taking certain creatine supplements shortly before the blood test can temporarily elevate serum creatinine and subsequently lower the estimated filtration rate. Furthermore, modern medicine is transitioning away from using race as a variable in these equations to ensure greater equity and accuracy for all patients.
Steps for Maintaining Kidney Health
Even with an excellent eGFR of 104, proactive steps can help ensure the long-term health of your kidneys. Managing blood pressure is one of the most effective actions, as uncontrolled high blood pressure is a leading cause of kidney damage over time. Keeping blood pressure consistently within a healthy range reduces the strain on the delicate blood vessels within the kidneys.
For individuals with diabetes or pre-diabetes, maintaining stable blood sugar levels is equally important to prevent kidney damage. High glucose concentrations force the kidneys to work harder, leading to long-term harm to the filtering units. Adequate hydration is also a simple but powerful tool, as drinking enough water helps the kidneys efficiently flush out waste products.
Another protective measure involves being mindful of medication use, particularly Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) like ibuprofen and naproxen. While safe for occasional use, chronic or excessive use of these medications can reduce blood flow to the kidneys, potentially causing injury. Regular physical activity and a balanced diet low in processed foods and sodium further support overall cardiovascular health, which directly benefits the kidneys.