The Physiological Decline of eGFR with Age
The estimated glomerular filtration rate (eGFR) is a key indicator of kidney health, measuring how effectively the kidneys filter waste products from the blood. However, eGFR levels naturally decline with age. This physiological reduction is a normal part of the aging process and does not automatically signal chronic kidney disease (CKD). For a 70-year-old, a normal eGFR is expected to be lower than it would be for a younger individual. Average eGFR levels for people over 70 tend to be around 75 mL/min/1.73 m², but individual results can vary significantly.
Research indicates that this decline is universal, typically beginning after age 40, and is partly caused by a gradual loss of nephrons—the kidney's filtering units. This natural aging process has led some experts to propose age-adapted thresholds for diagnosing CKD, as applying a one-size-fits-all threshold of 60 mL/min/1.73 m² to all age groups may lead to overdiagnosis in the elderly. For instance, a stable eGFR of 55 mL/min/1.73 m² in a 70-year-old without other complications may not require aggressive treatment for CKD, while the same reading in a younger person would be a greater cause for concern.
Interpreting eGFR Results in Older Adults
When a healthcare provider interprets an eGFR result for a 70-year-old, they look at several factors beyond the number itself. A result between 60 and 89 mL/min/1.73 m² may be considered normal in an elderly person, especially if there is no evidence of kidney damage, such as protein in the urine. To gain a clearer picture, doctors often check the urine for albumin, a type of protein, using a urine albumin-creatinine ratio (uACR) test.
If the eGFR is below 60, especially if it is consistently low for three months or more, and accompanied by other signs of kidney damage, it is more likely to indicate CKD. This is when closer monitoring and management, potentially by a nephrologist (kidney specialist), become necessary. The rate of decline is also a critical piece of information. A rapid decline is more worrying than a slow, gradual one and can be influenced by other health issues common in older age, like high blood pressure, diabetes, and smoking.
Factors That Can Influence eGFR in a 70-Year-Old
Several modifiable and non-modifiable factors can influence an eGFR reading in an older adult. Understanding these can help patients and their doctors interpret results more accurately.
- Chronic Conditions: Pre-existing conditions such as diabetes and hypertension are leading causes of kidney disease and can accelerate the decline in eGFR.
- Lifestyle Choices: Lifestyle factors play a significant role. Smoking is known to contribute to a faster decline in kidney function, and while BMI's impact is minimal in older adults, maintaining a healthy weight is beneficial.
- Cardiovascular Health: Impaired left ventricular systolic and diastolic function can be associated with a greater eGFR decline.
- Medications: Certain medications, including nonsteroidal anti-inflammatory drugs (NSAIDs), can be damaging to the kidneys and should be used cautiously. A doctor may need to adjust the dosage of medicines that are removed by the kidneys, particularly if eGFR is in the 60-89 range.
- Hydration and Diet: Dehydration can temporarily lower eGFR. Diet, including dietary protein intake, can also influence creatinine levels, which are used to calculate eGFR.
Comparison Table: Interpreting eGFR in Older vs. Younger Adults
| Characteristic | Younger Adults (e.g., 40-50 years) | Older Adults (e.g., 70+ years) |
|---|---|---|
| Average eGFR | Higher, around 99 mL/min/1.73 m² | Lower, around 75 mL/min/1.73 m² |
| eGFR 60-89 | Often indicates mild kidney damage or CKD, especially if persistent. | Can be normal due to age-related decline, especially without albuminuria. |
| eGFR <60 | Higher likelihood of indicating CKD stage 3 or higher. | More complex to interpret; may or may not signify clinically significant CKD depending on other health factors. |
| Clinical Focus | More aggressive management often pursued for CKD. | Individualized approach, balancing risks and other health concerns. |
| Albuminuria Test | Used to confirm kidney damage and aid in diagnosis. | Crucial for confirming if lower eGFR is due to disease or natural aging. |
Practical Recommendations for a 70-Year-Old
For a 70-year-old, understanding your eGFR is a step toward proactive health management. It's not just about the number but also the context. Here are some practical steps to consider:
- Track Trends, Not Just Numbers: Focus on the rate of change over time, not just a single test result. A stable, slightly lower eGFR is often less concerning than a rapidly declining one.
- Prioritize Overall Health: Managing blood pressure, controlling blood sugar levels if diabetic, and quitting smoking are highly effective strategies for preserving kidney function in later life.
- Maintain an Active Lifestyle: Regular, moderate physical activity can help manage underlying conditions that affect kidney health.
- Review Medications: Discuss all medications, including over-the-counter drugs, with your doctor to ensure they are not negatively impacting your kidney function.
- Don't Panic at a Lower eGFR: As studies have shown, a reading below 60 mL/min/1.73 m² does not automatically mean severe disease. A proper evaluation, including tests for albuminuria, is necessary for an accurate diagnosis.
Conclusion
What should the eGFR be for a 70 year old is not a simple question with a single answer. While an average eGFR for this age group is around 75 mL/min/1.73 m², interpreting any result requires a nuanced approach that considers the natural decline associated with aging. An eGFR between 60 and 89, particularly without albuminuria, may not indicate chronic kidney disease in an otherwise healthy older person. However, a result below 60, especially if persistent and accompanied by other indicators of kidney damage, warrants careful monitoring and management. For any 70-year-old, the most important aspect of managing kidney health is to maintain a dialogue with a healthcare provider, monitor health trends over time, and focus on overall cardiovascular and metabolic health to mitigate risks. An individualized model of care, rather than a rigid, disease-oriented approach, is most appropriate for many older adults.
