How is eGFR Calculated?

The estimated glomerular filtration rate (eGFR) is a critical measure for assessing kidney function, aiding in the diagnosis and management of kidney disease.

Formulas for Estimating eGFR

Three primary formulas are used to estimate eGFR:
1. Modification of Diet in Renal Disease (MDRD) Study equation
2. Cockcroft-Gault formula
3. Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation.

MDRD Study Equation

eGFR=175×(Serum Creatinine)^(−1.154)×(Age)^(−0.203)×(0.742 if Female)×(1.212 if African American)

Cockcroft-Gault Formula

CrCl=[(140−Age)×Weight×(0.85 if Female)]​ / [72×Serum Creatinine]

Where weight is in kilograms. While this formula estimates creatinine clearance (CrCl), it is closely related to eGFR and often used interchangeably in clinical practice.

CKD-EPI Equation

eGFR=141×min[(Serum Creatinine)​/k,1]^a ×max[(Serum Creatinine)/k,1)^(−1.209)×0.993^Age×(1.018 if Female)×(1.159 if African American)

Where 𝑘 is 0.7 for females and 0.9 for males, 𝑎 is -0.329 for females and -0.411 for males.

Common Usage

Among these formulas, the CKD Epidemiology Collaboration (CKD-EPI) equation is the most commonly used by laboratories. It offers more accurate eGFR estimates across different levels of kidney function, particularly at higher GFR levels, and is recommended by many clinical guidelines.

Example 1

Patient Details:
Serum Creatinine: 1.2 mg/dL
Age: 50 years
Sex: Female
Race: African American

CKD-EPI Calculation:
eGFR = 141× min(1.2/0.7,1)-0.329 × max(1.2/0.7,1)−1.209 × 0.99350 × 1.018 × 1.159
So, eGFR ≈ 61

Example 2

Patient Details:
Serum Creatinine: 0.9 mg/dL
Age: 65 years
Sex: Male
Race: Caucasian

MDRD Calculation:
eGFR = 175 × 0.9^(−1.154) × 65^(−0.203)
So, eGFR ≈ 85

Unit for eGFR

The unit for eGFR is mL/min/1.73m². It indicates the volume of blood (in milliliters) that the kidneys can filter per minute, normalized to a standard body surface area (BSA) of 1.73 square meters. This standardization allows for comparison across individuals of different sizes and body compositions, ensuring that the eGFR values are not biased by body size.

Quiz

1. Which equation is the most commonly used by laboratories to estimate eGFR due to its accuracy across different levels of kidney function?

2. What is the unit for the estimated glomerular filtration rate (eGFR)?

3. In the CKD-EPI equation, what are the values of k and a for males?

Please note that our articles are not intended to guide personal health decisions.

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