The kidneys, two bean-shaped organs located on either side of the spine, play an important role in maintaining overall health by filtering waste products and excess fluid from the blood. This essential process helps regulate blood pressure, produce red blood cells, and keep bones healthy. A key measure of how well these vital organs are functioning is the Glomerular Filtration Rate, or GFR. Monitoring GFR provides an indication of kidney health and helps detect issues early.
What is GFR and Why It Matters
The Glomerular Filtration Rate (GFR) measures how quickly blood is filtered by the kidneys. This filtration process primarily occurs in tiny structures within the kidneys called glomeruli. Each kidney contains millions of nephrons, and a glomerulus, a network of small blood vessels, is at the beginning of each nephron. Blood enters the glomerulus, where waste products, toxins, and excess water are filtered out to form a fluid called filtrate.
This filtrate then proceeds through the kidney tubules to ultimately become urine. Maintaining a healthy GFR is important because it ensures that waste products like urea and creatinine do not accumulate in the body. It also helps regulate fluid balance and electrolyte levels. A consistent GFR indicates the kidneys are effectively performing their cleansing function, making it a key indicator doctors use to assess kidney health.
GFR Levels and Age
Glomerular Filtration Rate naturally declines with age, even in individuals without kidney disease. This decline often begins around 30 to 40 years of age. For younger adults, a GFR value of 90 milliliters per minute per 1.73 square meters (mL/min/1.73 m2) or higher is considered normal.
GFR values gradually decrease with age. For instance, values between 60-89 mL/min/1.73 m2 may be considered normal for older adults, especially if there are no other signs of kidney damage. While a GFR below 60 mL/min/1.73 m2 suggests chronic kidney disease, this may be less concerning in healthy adults over 70, where such values can be typical. What is normal for a 20-year-old may differ from what is typical for a 70-year-old.
Other Factors Influencing GFR
Beyond aging, several other factors can impact an individual’s GFR. Chronic health conditions like diabetes and high blood pressure are common causes of kidney disease and can reduce GFR over time. These conditions can damage the filtering units within the kidneys. Certain medications, including nonsteroidal anti-inflammatory drugs (NSAIDs) and some antibiotics, can also temporarily or permanently affect kidney function and lower GFR.
Acute events like severe dehydration can drastically reduce GFR because the kidneys require adequate fluid volume to filter blood efficiently. Specific kidney diseases, infections, or obstructions in the urinary tract can also impede filtration. Additionally, factors such as body size, muscle mass, pregnancy, and even diet can influence creatinine levels, which are used to estimate GFR, thereby indirectly affecting the calculated rate.
Understanding Your GFR Results
Glomerular Filtration Rate is typically not measured directly but is estimated using a blood test that assesses creatinine, a waste product from muscle metabolism. This creatinine level, along with other parameters like age and sex, is then fed into mathematical formulas to calculate an estimated GFR (eGFR). The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is widely used for this purpose.
The inclusion of race in eGFR calculations has been a subject of discussion and controversy. Historically, some formulas included a race variable based on assumptions about muscle mass differences, but major kidney organizations now recommend removing this factor to promote health equity. An eGFR below 60 mL/min/1.73 m2 for three months or more often indicates chronic kidney disease. A single GFR reading is merely a snapshot; healthcare professionals consider trends over time and other clinical information for a comprehensive assessment of kidney health and personalized guidance.