A low estimated Glomerular Filtration Rate (eGFR) on a blood test indicates kidney health. This measurement helps healthcare providers assess how effectively your kidneys filter waste from your blood. Understanding what eGFR signifies and interpreting a low result can guide steps toward maintaining kidney well-being.
What eGFR Represents
The eGFR, or estimated Glomerular Filtration Rate, is a calculated value that reflects how well your kidneys are filtering waste. The kidneys contain tiny filters called glomeruli, which are responsible for removing waste and excess water from your blood to produce urine. The eGFR specifically estimates the amount of blood these glomeruli clean each minute.
The calculation of eGFR relies on a blood test that measures creatinine levels. Creatinine is a waste product from muscle wear and tear and dietary protein digestion. Age, sex, and body type are also incorporated into the formula for a more accurate estimate. While eGFR is an estimate, its accuracy can be influenced by factors like muscle mass, diet, and certain medical conditions.
Interpreting Low eGFR Levels
A low eGFR indicates that your kidneys may not be filtering blood as efficiently as they should. For adults, an eGFR value is around 100 mL/min/1.73m², with values decreasing with age even in the absence of kidney disease. A consistently low eGFR, especially if it remains below 60 mL/min/1.73m² for three months or longer, can suggest chronic kidney disease (CKD).
Chronic kidney disease is categorized into five stages based on eGFR ranges:
- Stage 1: eGFR of 90 mL/min/1.73m² or higher, often with other signs of kidney damage (e.g., protein in urine).
- Stage 2: eGFR between 60 and 89 mL/min/1.73m², also with other signs of kidney damage.
- Stage 3: Moderately reduced kidney function, eGFR 30-59 mL/min/1.73m². This stage is divided into Stage 3a (45-59 mL/min/1.73m²) and Stage 3b (30-44 mL/min/1.73m²).
- Stage 4: Severe kidney damage, eGFR 15-29 mL/min/1.73m².
- Stage 5: Kidney failure, eGFR below 15 mL/min/1.73m².
Why eGFR Levels Can Be Low
Several factors can contribute to lower eGFR levels, ranging from chronic health conditions to acute situations. Chronic kidney disease (CKD) is a common cause, where kidney damage occurs over an extended period, leading to a sustained decline in eGFR. This type of damage is irreversible.
Common underlying chronic conditions that can lead to reduced eGFR include diabetes and high blood pressure (hypertension). Both can damage the tiny filtering units within the kidneys over time. Other kidney diseases, such as polycystic kidney disease (growth of cysts) and glomerulonephritis (inflammation of kidney filters), can also impair kidney function. Acute kidney injury (AKI), a sudden episode of kidney damage, can cause a rapid, temporary drop in eGFR. Certain medications, such as non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, can also affect kidney function, especially with high doses or prolonged use.
Steps After a Low eGFR Result
Receiving a low eGFR result warrants a follow-up with a healthcare professional to determine the underlying cause and appropriate course of action. Your doctor may recommend additional tests, such as a urinalysis to check for protein or blood in the urine, or imaging tests like an ultrasound or CT scan to visualize the kidneys. These tests help to assess the extent of kidney damage and identify specific conditions.
Many individuals with early-stage CKD experience no noticeable symptoms because the kidneys can compensate for reduced function. However, as kidney issues progress, symptoms might emerge, including fatigue, swelling in the ankles, feet, or hands due to fluid retention, changes in urination patterns, and itchy skin. Nausea, loss of appetite, and muscle cramps can also occur.
Managing a low eGFR often involves lifestyle adjustments and addressing underlying health conditions. This can include adopting a balanced diet low in sodium, processed foods, and unhealthy fats, while increasing consumption of fruits, vegetables, and whole grains. Regular physical activity and maintaining a healthy weight can also support kidney health. Controlling blood pressure and blood sugar levels, if you have hypertension or diabetes, is also important to prevent further kidney damage. Your doctor may also review your medications, adjusting dosages or recommending alternatives if certain drugs are impacting kidney function.