The Glomerular Filtration Rate (GFR) is a crucial measure of how well your kidneys are functioning. It estimates the amount of blood that passes through the glomeruli (tiny filters in your kidneys) each minute. A healthy GFR means your kidneys are effectively removing waste products and excess fluid from your blood.
Why is GFR Important?
Early Detection of Kidney Disease: A declining GFR is often the earliest sign of kidney damage, even before symptoms appear.
Staging Chronic Kidney Disease (CKD): GFR values are used to classify the stage of CKD, which helps healthcare providers determine the best course of treatment and monitor disease progression.
Medication Dosing: Many medications are cleared by the kidneys. Knowing a patient's GFR helps doctors adjust drug dosages to prevent accumulation and toxicity.
Overall Health Assessment: Kidney health is linked to cardiovascular health and other systemic conditions.
How is GFR Calculated?
Directly measuring GFR is complex and usually involves injecting a tracer substance. Therefore, GFR is typically estimated using formulas that incorporate readily available blood test results, primarily serum creatinine, along with age, sex, and sometimes other factors.
Several equations exist for estimating GFR, including the Cockcroft-Gault, MDRD (Modification of Diet in Renal Disease), and CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equations. The CKD-EPI equations are currently recommended by many professional organizations due to their improved accuracy, especially at higher GFR values.
This calculator uses the CKD-EPI 2021 equation, which is an updated version that removes the race coefficient, making it more equitable and widely applicable. The inputs required are:
Serum Creatinine (mg/dL): Creatinine is a waste product from muscle metabolism. Healthy kidneys filter it out of the blood. Higher levels can indicate reduced kidney function.
Age (years): Kidney function naturally declines with age.
Sex: Biological sex influences muscle mass and creatinine production, which are factors in the GFR calculation.
Interpreting Your GFR Results (CKD Stages)
GFR is measured in milliliters per minute per 1.73 square meters (mL/min/1.73m²), which adjusts the result for average body surface area. Here's a general guide to CKD stages based on GFR:
G1: GFR ≥ 90 mL/min/1.73m² – Normal or High GFR. No or minimal kidney damage.
G2: GFR 60-89 mL/min/1.73m² – Mildly Decreased GFR. Mild kidney damage may be present.
G3a: GFR 45-59 mL/min/1.73m² – Mildly to Moderately Decreased GFR.
G3b: GFR 30-44 mL/min/1.73m² – Moderately to Severely Decreased GFR.
G4: GFR 15-29 mL/min/1.73m² – Severely Decreased GFR. Preparation for kidney replacement therapy may be needed.
G5: GFR < 15 mL/min/1.73m² – Kidney Failure. Dialysis or kidney transplant is typically required.
It's important to note that a GFR result should always be interpreted by a healthcare professional in the context of your overall health, medical history, and other diagnostic tests. This calculator is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.