What is gfr in blood test
Last updated: April 1, 2026
Key Facts
- GFR measures the volume of blood filtered by kidney glomeruli per minute (normal range: 60-100 mL/min)
- GFR is calculated from blood creatinine levels using predictive equations like CKD-EPI or MDRD
- A GFR below 60 may indicate kidney disease and requires medical evaluation
- GFR decline is gradual and often asymptomatic until advanced stages
- Regular GFR testing is essential for people with diabetes, hypertension, or family history of kidney disease
Understanding GFR
Glomerular Filtration Rate (GFR) is a critical measure of kidney function that indicates how many milliliters of blood your kidneys filter through the glomeruli (tiny filtering units) each minute. A healthy GFR is typically 60 mL/min/1.73m² or higher in adults. This measurement helps doctors assess kidney health and screen for chronic kidney disease. GFR naturally declines with age, but a sharp or rapid decline indicates kidney problems.
How GFR is Calculated
GFR cannot be directly measured, so it's calculated using blood test results, primarily serum creatinine levels. Common calculation methods include:
- CKD-EPI equation: The most current and accurate formula, considering age, sex, and race
- MDRD equation: An older but still-used formula for calculating GFR
- Cockcroft-Gault formula: Sometimes used, particularly for medication dosing
- Cystatin C: An alternative marker when creatinine is unreliable
- 24-hour urine collection: Direct measurement method, though rarely used today
GFR and Kidney Disease Stages
GFR values determine chronic kidney disease (CKD) stages:
- Stage 1 (GFR ≥90): Normal or high kidney function
- Stage 2 (GFR 60-89): Mild decrease in kidney function
- Stage 3a (GFR 45-59): Mild to moderate decrease
- Stage 3b (GFR 30-44): Moderate to severe decrease
- Stage 4 (GFR 15-29): Severe decrease
- Stage 5 (GFR <15): Kidney failure, dialysis usually needed
Factors Affecting GFR
Several factors influence GFR values and kidney function: age (GFR naturally declines with age), sex (differences in muscle mass and creatinine production), diet (high protein can temporarily elevate creatinine), medications, and hydration status. Diseases like diabetes, hypertension, and autoimmune conditions also damage kidneys and lower GFR over time.
Importance of Regular Monitoring
For people with risk factors like diabetes or hypertension, regular GFR testing helps detect kidney disease early. Early detection enables interventions to slow progression and prevent the need for dialysis or kidney transplant. Even small declines in GFR warrant medical attention and evaluation.
Related Questions
What does a low GFR mean?
A low GFR indicates decreased kidney function and possible kidney disease. A GFR below 60 warrants further evaluation by a doctor. The lower the GFR, the worse the kidney function, with values below 15 indicating kidney failure.
What causes GFR to decrease?
GFR decreases with age naturally, but rapid decline usually indicates kidney disease caused by diabetes, hypertension, chronic kidney disease, autoimmune conditions, or other factors. Certain medications can also affect GFR.
How can I improve my GFR?
GFR improvement depends on the underlying cause. Managing blood pressure, controlling diabetes, reducing protein intake, maintaining healthy weight, avoiding NSAIDs, and staying hydrated can help slow GFR decline. Medications like ACE inhibitors may also help protect kidney function.
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Sources
- National Institute of Diabetes and Digestive and Kidney Diseases - GFR Public Domain
- Wikipedia - Glomerular Filtration Rate CC-BY-SA-4.0