GFR Calculator

Understanding Glomerular Filtration Rate (GFR)

Glomerular Filtration Rate (GFR) describes the rate of flow of filtered fluids through the kidney and is used as a measure of kidney function. Generally, a higher value of GFR indicates better kidney function. A significant decrease in GFR indicates that the kidney is not properly functioning, resulting in lower volumes of fluids being filtered over a given time.

The normal range of GFR adjusted for body surface area is 100 to 130 mL/min/1.73m² in men and 90 to 120 mL/min/1.73m² in women below the age of 40. After age 40, GFR decreases progressively with age.

GFR Calculation Formulas

IDMS-Traceable MDRD Study Equation

GFR = 175 × (SCr)^-1.154 × (age)^-0.203 × (0.742 if female) × (1.212 if Black)

Where SCr = serum creatinine in mg/dL

CKD-EPI Formula

GFR varies based on gender, race, and creatinine level

More accurate than MDRD, especially at higher GFR levels

Mayo Quadratic Formula

GFR = e^(1.911 + 5.249/SCr - 2.114/SCr² - 0.00686 × age - (0.205 if female))

If SCr < 0.8 mg/dL, use 0.8 mg/dL for SCr

Schwartz Formula (Children)

GFR = 0.413 × height(cm) / SCr

Used for children 18 years and younger

Population Mean Estimated GFR by Age

Age	Mean Estimated GFR (mL/min/1.73 m²)
20-29	116
30-39	107
40-49	99
50-59	93
60-69	85
70+	75

Chronic Kidney Disease (CKD) Stages

Stage	GFR Value (mL/min/1.73 m²)	Description	Clinical Action
Normal	90+ and no proteinuria	Normal kidney function	Screening, CKD risk reduction
CKD Stage 1	90+ with kidney damage	Kidney damage with normal GFR	Diagnosis and treatment, CVD risk reduction
CKD Stage 2	60-89 with kidney damage	Mild decrease in GFR	Estimating progression
CKD Stage 3	30-59	Moderate decrease in GFR	Evaluating and treating complications
CKD Stage 4	15-29	Severe decrease in GFR	Preparation for kidney replacement therapy
CKD Stage 5	<15	Kidney failure	Kidney replacement (if uremia present)

Factors Affecting GFR

		Age: GFR naturally decreases with age, approximately 1 mL/min/1.73m² per year after age 40.
	

		Gender: Men typically have higher GFR values than women due to larger muscle mass and body size.
	

		Race: Black individuals may have higher creatinine levels due to increased muscle mass, affecting GFR calculations.
	

		Muscle Mass: Higher muscle mass increases serum creatinine, potentially underestimating GFR in muscular individuals.
	

Clinical Significance of GFR

Kidney Function Assessment: GFR is the best overall measure of kidney function. It helps determine how well the kidneys are filtering waste and excess water from the blood.

Disease Staging: GFR values are used to stage chronic kidney disease, helping guide treatment decisions and monitoring disease progression.

Drug Dosing: Many medications require dose adjustments based on kidney function. GFR helps healthcare providers prescribe safe and effective medication doses.

Treatment Planning: GFR values help determine when to start specific treatments, such as preparing for dialysis or kidney transplantation.

Limitations of GFR Estimation

		Creatinine-Based Limitations: All creatinine-based formulas have limitations in certain populations, including those with very high or low muscle mass, amputees, or those following vegetarian diets.
	

		Acute Changes: GFR estimates may not accurately reflect kidney function during acute illness or rapid changes in kidney function.
	

		Medication Effects: Some medications can affect creatinine levels without changing actual kidney function.
	

Improving Kidney Health

Blood Pressure Control: Maintaining normal blood pressure (less than 130/80 mmHg) helps protect kidney function and slow progression of kidney disease.

Diabetes Management: Keeping blood sugar levels well-controlled reduces the risk of diabetic kidney disease and protects existing kidney function.

Healthy Lifestyle: Regular exercise, maintaining a healthy weight, not smoking, and limiting alcohol consumption all support kidney health.

Medication Awareness: Avoiding overuse of NSAIDs (like ibuprofen) and being cautious with other potentially nephrotoxic medications helps preserve kidney function.

Regular Monitoring: Regular check-ups including blood pressure, blood sugar, and kidney function tests help detect problems early when treatment is most effective.

		Important Note: GFR estimates should always be interpreted in the clinical context by healthcare professionals. This calculator is for educational purposes and should not replace professional medical advice, diagnosis, or treatment.
	