The kidneys function as the body’s filtration system, constantly working to remove waste products and excess fluid from the blood. The efficiency of this process is quantified by the Glomerular Filtration Rate (GFR). Kidney function naturally changes over a person’s lifespan, typically showing a gradual decline with age. Understanding the GFR is important for older adults, as the interpretation of results shifts depending on age. This article clarifies what the GFR number represents and what constitutes a typical range for someone around 70 years old.
Understanding Glomerular Filtration Rate and Its Measurement
The GFR measures the flow rate of fluid filtered from the blood into the kidney tubules, reflecting the volume of blood the kidneys clean per minute. Since measuring the true GFR is complex, healthcare providers rely on the estimated GFR (eGFR), calculated using a formula based on a simple blood test measuring creatinine levels.
Creatinine is a waste product generated by muscle metabolism. Healthy kidneys efficiently filter creatinine out of the bloodstream; when function declines, creatinine levels rise, signaling less efficient filtration. The eGFR calculation, often using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula, incorporates the serum creatinine value alongside a person’s age and sex.
These demographic factors are included because creatinine production is influenced by muscle mass, which often decreases with age. The eGFR value is standardized to a body surface area of 1.73 square meters for comparison between individuals.
GFR Norms for Older Adults and Staging of Kidney Function
For a healthy young adult, GFR is typically between 90 and 120 mL/min/1.73m², but this naturally decreases over time. A GFR in the range of 60 to 89 is often considered mildly decreased, but may be interpreted as normal for an adult over 65 years old due to physiological changes.
For a person around 70 years old, an average eGFR can be around 75, and values between 50 and 70 are often considered typical due to aging. However, a GFR consistently below 60 for three months or more is the threshold for diagnosing Chronic Kidney Disease (CKD), regardless of age. CKD is categorized into stages based on the GFR result.
CKD Staging
CKD Stage 1 is an eGFR of 90 or higher, diagnosed only if there is other evidence of kidney damage, such as protein in the urine. Stage 2 ranges from 60 to 89, also requiring signs of damage for a CKD diagnosis. Stage 3 is divided into two sub-stages: Stage 3a (45 to 59) and Stage 3b (30 to 44). Stage 4 represents severely decreased function (15 to 29), and Stage 5 is kidney failure (below 15).
Non-Age Related Factors That Affect GFR Results
While age accounts for a predictable decline, many other factors can cause GFR to drop or fluctuate, complicating the interpretation of a single lab result. Uncontrolled high blood pressure (hypertension) and diabetes are primary causes of kidney damage. Hypertension harms the delicate filtering units, while consistently high blood sugar from diabetes gradually damages the small blood vessels, impairing filtration capacity.
Certain common medications can also influence GFR. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen can reduce blood flow to the kidneys, leading to a temporary drop in GFR, especially with chronic use. Acute conditions, particularly dehydration, can significantly and quickly lower the GFR by reducing the blood volume available for filtration.
The eGFR calculation assumes stability. Factors like a recent high-protein meal or a significant change in muscle mass can temporarily raise or lower creatinine levels, causing a misleading result. Therefore, a diagnosis of chronic kidney disease requires a low GFR to persist for at least three months, confirming the change is not due to a temporary event.
Strategies for Supporting Kidney Health
Proactive lifestyle and medical management can help maintain GFR and slow age-related decline. Managing existing conditions, particularly high blood pressure and diabetes, is the most impactful step, as these are the leading causes of kidney damage. Controlling blood pressure, often aiming for levels below 130/80 mmHg, protects the internal kidney structures.
Maintaining adequate hydration is beneficial, as water helps the kidneys flush out waste products. Patients should discuss the use of over-the-counter pain relievers like NSAIDs with a doctor, as long-term use poses a risk to kidney function.
A kidney-friendly diet generally involves reducing sodium intake to help control blood pressure. For those with established kidney concerns, a doctor may recommend monitoring protein, potassium, and phosphorus intake. Regular physical activity supports cardiovascular health, which maintains healthy blood flow to the kidneys.