The estimated Glomerular Filtration Rate (eGFR) is a calculation derived from a simple blood test that helps assess kidney function. This measurement indicates how effectively your kidneys are filtering waste products from your blood. Specifically, it quantifies the rate at which tiny filters within your kidneys, called glomeruli, clean the blood each minute. Understanding your eGFR is a recognized part of maintaining overall health, providing insight into the performance of these vital organs. This number offers a way for healthcare providers to gauge kidney health and identify potential concerns early.
Understanding Your eGFR Number
Your eGFR result provides an estimate of your kidney function, and this number is often used to determine the stage of chronic kidney disease (CKD) if kidney damage is present. A higher eGFR number generally indicates better kidney function. An eGFR of 90 milliliters per minute per 1.73 square meters of body surface area or higher is typically considered normal kidney function, though other signs of kidney damage might still be present.
When the eGFR falls between 60 and 89 mL/min/1.73m², it suggests mildly decreased kidney function, categorizing it as Stage 2 CKD. A value ranging from 45 to 59 mL/min/1.73m² indicates Stage 3a, representing a mild to moderate decrease in kidney function. Further decline to an eGFR between 30 and 44 mL/min/1.73m² corresponds to Stage 3b, signifying a moderately to severely decreased function.
An eGFR between 15 and 29 mL/min/1.73m² places individuals in Stage 4 CKD, indicating severely decreased kidney function where waste products can accumulate. The final classification, Stage 5 CKD, occurs when the eGFR drops below 15 mL/min/1.73m², consistent with kidney failure. Early identification of these stages allows for management strategies to slow the progression of kidney issues.
Factors That Influence eGFR Results
The eGFR is an estimate, meaning several factors beyond kidney disease can influence its numerical value. Age is a significant variable, as eGFR naturally declines as a person gets older, even without kidney disease. The calculation relies on creatinine levels, a waste product from muscle metabolism, so individual muscle mass can affect the result; people with higher muscle mass might have higher creatinine levels, potentially leading to a lower eGFR estimate despite healthy kidneys.
Acute illnesses, dehydration, and a high-protein diet can temporarily impact creatinine levels and, consequently, the eGFR. Certain medications also have the potential to influence eGFR readings by affecting creatinine levels or kidney function directly. Given these variables, healthcare providers often consider trends in eGFR over time rather than focusing on a single measurement.
It is also important to note recent changes in the eGFR calculation formula. Historically, race was included as a variable, but medical organizations have moved to race-neutral equations. This adjustment recognizes that race is a social construct, and its inclusion could potentially mask kidney disease in certain populations, prompting a shift towards more equitable and accurate assessments for all individuals.
The Role of Albuminuria in Kidney Assessment
While eGFR measures the kidney’s filtering performance, another important test, albuminuria, provides direct evidence of kidney damage. Albuminuria refers to the presence of albumin, a type of protein, in the urine. Healthy kidneys are designed to keep albumin in the blood, allowing very little, if any, to pass into the urine.
If the kidney’s filters are damaged, albumin can leak through and appear in the urine, even if the eGFR is still within a normal range. This situation is comparable to assessing a car’s engine: eGFR measures how well the engine is running, while albuminuria is like seeing smoke coming from the exhaust, indicating a problem regardless of how smoothly the engine sounds. Therefore, medical professionals consider both eGFR and albuminuria together to gain a comprehensive understanding of kidney health and to determine the stage of kidney disease. This combined assessment allows for a more accurate risk evaluation, helping to guide treatment and monitoring strategies.
Interpreting Low eGFR Results
Receiving a low eGFR result can be concerning, but a single reading, especially if only slightly below the normal range, does not automatically confirm kidney disease. Healthcare providers typically evaluate trends in eGFR over multiple tests and time periods to determine if a sustained decrease in kidney function is present. A diagnosis of chronic kidney disease usually requires an eGFR below 60 mL/min/1.73m² for three months or longer, or an eGFR above 60 with other signs of kidney damage.
The next step upon receiving any eGFR result is to discuss it with your healthcare provider. They may recommend repeat testing to confirm the initial finding or order additional evaluations. These might include a urinalysis to check for protein or blood in the urine, or imaging tests such as a kidney ultrasound to visualize the kidneys’ structure. This collaborative approach ensures proper interpretation and appropriate follow-up care.