What is eGFR?
Estimated Glomerular Filtration Rate (eGFR) is a measure of how well your kidneys are filtering waste products from your blood. The test uses a blood sample to measure the level of creatinine, a waste product from muscle metabolism, and incorporates a formula that accounts for your age, sex, and other factors. A lower eGFR indicates reduced kidney function.
The role of physiological aging
As a person ages beyond 30, the GFR naturally and progressively declines at an average rate of about 8 mL/min/1.73 m² per decade. This is a normal part of the aging process, reflecting the gradual loss of functioning nephrons, the kidney's filtering units. For many healthy elderly individuals, a moderately low eGFR, even below 60 mL/min/1.73 m², may not indicate a serious disease but rather normal kidney senescence.
Chronic health conditions as a primary driver
While aging is a factor, underlying chronic diseases are the most significant contributors to a rapid or pronounced low eGFR in the elderly.
Common diseases that impact kidney function:
- Hypertension (high blood pressure): The second leading cause of kidney disease. Uncontrolled high blood pressure can narrow and harden the blood vessels leading to the kidneys, reducing blood flow and filtering efficiency. Research shows higher systolic blood pressure is linked to a faster decline in eGFR in older individuals.
- Diabetes: Excess glucose in the blood can damage the tiny filters within the kidneys (glomeruli), which is a common cause of chronic kidney disease. Both type 1 and type 2 diabetes pose a risk.
- Heart disease: Cardiovascular conditions like heart failure and atherosclerosis can reduce blood flow to the kidneys, leading to decreased function. The heart and kidneys have an interconnected relationship, with one's dysfunction affecting the other.
- Obesity: Excess weight, particularly obesity, places a greater strain on the kidneys. It is a risk factor that can contribute to and accelerate the decline in eGFR.
Impact of medications and lifestyle factors
Certain medications and lifestyle choices can also cause or worsen a low eGFR in older adults. Frail older patients are often on multiple medications, a condition known as polypharmacy, which increases the risk of side effects, including kidney damage.
Medications that can affect eGFR:
- Non-steroidal anti-inflammatory drugs (NSAIDs): Over-the-counter pain relievers like ibuprofen and naproxen can damage the kidneys, especially with long-term use, higher doses, or when a person is dehydrated.
- Diuretics: These medications increase urination but can cause dehydration if fluid intake isn't managed, temporarily lowering eGFR.
- Certain antibiotics: Some types, including aminoglycosides and vancomycin, are known to have nephrotoxic (kidney-damaging) effects.
- Proton Pump Inhibitors (PPIs): Long-term use of these antacids has been linked to kidney damage.
Lifestyle factors:
- Smoking: Tobacco use damages blood vessels, restricting blood flow to the kidneys and accelerating the decline of kidney function.
- Dehydration: Not drinking enough water reduces blood volume, making it harder for the kidneys to function properly and causing a temporary drop in eGFR.
- High-sodium diet: High salt intake is linked to higher blood pressure, which, as mentioned, negatively affects kidney health.
Differentiating normal aging from disease
Diagnosing the cause of a low eGFR requires careful consideration by a healthcare provider. They must distinguish between normal age-related decline and pathological disease. While moderate eGFR reduction is common in the elderly, a sustained low eGFR accompanied by other signs, such as proteinuria (protein in the urine), may indicate chronic kidney disease.
Comparison: Normal Age-Related Decline vs. Chronic Kidney Disease (CKD)
| Feature | Normal Age-Related Decline | Chronic Kidney Disease (CKD) |
|---|---|---|
| eGFR Reduction | Gradual, slow decline over decades. | Faster, more pronounced decline. |
| Presence of Proteinuria | Typically absent. | Often present (protein in urine). |
| Associated Symptoms | Often asymptomatic. | Can include fatigue, swelling, or changes in urination. |
| Underlying Cause | Physiological nephron loss. | Often caused by diabetes, hypertension, or inflammation. |
| Prognosis | Generally favorable, not progressing to kidney failure. | Varies, but risk of progression is higher. |
What happens next? Management and prognosis
For elderly patients with low eGFR, management focuses on controlling underlying conditions and modifying risk factors. For some, especially those with minimal albuminuria and a stable, slow decline, the prognosis is favorable, and management can be less aggressive. For others, especially those with associated cardiovascular disease, intensive monitoring and treatment are necessary. A kidney-friendly diet low in sodium, regular physical activity, and avoiding nephrotoxic medications are standard recommendations.
In conclusion, low eGFR in the elderly is a multifactorial issue. It is driven by the natural process of kidney aging but is profoundly influenced by chronic diseases like hypertension and diabetes. Understanding the specific cause is critical for effective management and preventing further kidney damage, as well as considering an individual's overall health and frailty.
Understanding chronic kidney disease
Conclusion
While a decrease in eGFR is expected with age, a low eGFR in the elderly is more than just a sign of getting older. It often signals underlying conditions that put significant strain on the kidneys, such as unmanaged high blood pressure, diabetes, or heart disease. Certain medications and unhealthy lifestyle habits also accelerate this decline. Effective management requires distinguishing between normal physiological aging and chronic kidney disease, focusing on controlling underlying risk factors, and adopting kidney-protective lifestyle habits. This personalized approach is crucial for preserving kidney function and ensuring the best possible quality of life for older adults.
