The estimated Glomerular Filtration Rate (eGFR) is a calculation used to assess how well the kidneys filter waste products from the blood. This measurement reflects the rate at which blood passes through the glomeruli, the tiny filtering units within the kidney. A low eGFR suggests the kidneys are not clearing waste efficiently, potentially signaling kidney damage or disease. Since a reduced filtration rate often progresses silently, this estimate helps healthcare providers monitor kidney health and determine the appropriate course of action.
Understanding eGFR Measurement and Staging
The eGFR is an estimate of the true Glomerular Filtration Rate (GFR), which is too complex to measure directly for routine care. A standardized formula calculates the eGFR using variables like the level of creatinine in the blood, along with the patient’s age and sex. Creatinine is a waste product from normal muscle breakdown that healthy kidneys efficiently remove.
If the kidneys are damaged, creatinine levels rise, causing the eGFR value to drop. The result is reported in milliliters per minute per 1.73 meters squared, adjusting for average body surface area. Older formulas that included race are being discontinued in many medical settings to ensure greater equity and accuracy.
Healthcare professionals use the eGFR result to stage Chronic Kidney Disease (CKD) based on the degree of filtration loss. An eGFR of 90 or above is generally considered normal, though other signs of damage may indicate early disease. A result between 60 and 89 represents a mild decrease, and an eGFR below 60 for three months or more is a definitive marker for CKD.
The staging system continues with decreasing function: Stage 3 (moderate to severe loss) is split into 3a (45-59) and 3b (30-44). Stage 4 marks severe loss (15-29), and Stage 5 indicates kidney failure (below 15). This staging guides treatment decisions and helps predict the risk of complications.
Major Underlying Conditions That Reduce eGFR
Most chronic kidney disease cases resulting in a low eGFR are linked to long-term systemic diseases that damage the kidney’s internal structures. Diabetes is the leading cause, as chronically high blood sugar levels injure the tiny blood vessels (capillaries) that form the filtering units. This exposure causes scarring and thickening of the glomeruli (glomerulosclerosis), leading to protein leakage and a progressive reduction in filtering ability.
High blood pressure (hypertension) is the second most common cause of a declining eGFR. Uncontrolled high pressure forces blood through the kidney’s vessels, causing them to stiffen, narrow, and weaken. This damage makes the filtering process less efficient, which accelerates kidney damage and makes blood pressure regulation harder.
Other diseases can also reduce eGFR, such as Glomerulonephritis, which involves inflammation of the glomeruli often caused by immune disorders. Polycystic Kidney Disease (PKD) is a genetic disorder where fluid-filled cysts grow in the kidneys, gradually replacing healthy tissue. In all these conditions, the underlying mechanism is the destruction of the kidney’s functional units.
Physical Signs of Decreased Kidney Function
Early-stage CKD is often silent because the body compensates for significant function loss without noticeable symptoms. As the eGFR falls into moderate and severe stages, waste products and excess fluid accumulate, leading to physical manifestations. Swelling (edema) is common in the feet, ankles, or legs due to the reduced ability to remove sodium and water.
Persistent fatigue and weakness result from the buildup of toxins in the bloodstream. Changes in urination patterns include needing to urinate more frequently, especially at night, or noticing foamy urine. Foamy urine indicates a high level of protein escaping through damaged kidney filters.
Low eGFR can also cause cognitive changes, such as difficulty concentrating or mental fog. These imbalances affect the nervous system when the body cannot properly balance minerals and remove waste. Additionally, the skin may become dry and itchy due to mineral and bone disorders associated with advanced function loss.
Treatment and Management Approaches
Management of a low eGFR focuses on slowing damage progression through medical intervention and lifestyle changes. Medical treatment often includes specific blood pressure medications, even if pressure is only mildly elevated, due to their protective effect on kidney filters. Angiotensin-converting enzyme (ACE) inhibitors and Angiotensin II receptor blockers (ARBs) are frequently prescribed to reduce pressure within the glomeruli and lessen protein leakage.
For diabetic individuals, tight blood sugar control is primary to prevent further damage. Newer drug classes, such as SGLT-2 inhibitors, are increasingly used because they slow eGFR decline and reduce cardiovascular risk. All medication dosages for chronic conditions must be carefully adjusted based on the current eGFR to prevent drug accumulation.
Lifestyle adjustments are important for preserving remaining kidney function. Dietary modification typically involves restricting sodium intake (often below 2,300 mg per day) to control blood pressure and reduce fluid retention. Protein intake may also need moderation (around 0.8 grams per kilogram of body weight per day) in consultation with a renal dietitian, to minimize the workload on the filtering units.
Harmful Substances and Advanced Care
Avoiding substances that harm the kidneys is necessary, including non-steroidal anti-inflammatory drugs (NSAIDs), which should be used cautiously or avoided. Smoking cessation is also advised, as tobacco use constricts blood vessels and accelerates function loss. Patients whose eGFR falls below 30 require referral to a nephrologist to coordinate advanced care.