Calculation of eGFR for a 50-Year-Old Male with Serum Creatinine of 0.73 mg/dL
The eGFR for this 50-year-old male weighing 58 kg with serum creatinine of 0.73 mg/dL is approximately 113 mL/min/1.73 m² using the CKD-EPI equation, which indicates normal kidney function (Stage G1).
Calculation Methods
There are several established methods to calculate eGFR, with the most commonly used being:
1. CKD-EPI Equation (2009) - Recommended Method
The CKD-EPI equation is currently the preferred method for estimating GFR as recommended by guidelines 1:
For males with serum creatinine ≤0.9 mg/dL: eGFR = 141 × (Scr/0.9)^-0.411 × 0.993^age
For this patient: eGFR = 141 × (0.73/0.9)^-0.411 × 0.993^50 = 113 mL/min/1.73 m²
2. Cockcroft-Gault Formula
This formula calculates creatinine clearance rather than GFR 1:
CrCl (mL/min) = [(140 - age) × weight (kg)] / [72 × serum creatinine (mg/dL)] CrCl = [(140 - 50) × 58] / [72 × 0.73] = 92.3 mL/min
Note: This is not adjusted for body surface area like the other formulas.
3. MDRD Study Equation
The 4-variable MDRD equation 1:
eGFR (mL/min/1.73 m²) = 186 × [serum creatinine (mg/dL)]^-1.154 × [age]^-0.203 × [0.742 if female] × [1.21 if Black]
For this patient: eGFR = 186 × [0.73]^-1.154 × 50^-0.203 = 107 mL/min/1.73 m²
Interpretation of Results
Based on the calculated eGFR of 113 mL/min/1.73 m² using the CKD-EPI equation:
- This value falls into CKD Stage G1 (≥90 mL/min/1.73 m²), indicating normal kidney function 1
- According to the National Kidney Foundation guidelines, this would be described as "Your kidneys are filtering at full strength" 2
- No evidence of kidney disease is present based solely on this eGFR value
Clinical Considerations
- The CKD-EPI equation is preferred over MDRD for patients with normal or mildly decreased kidney function 1, 2
- For complete CKD assessment, urinary albumin-to-creatinine ratio should also be measured, as albuminuria is an important marker of kidney damage even when eGFR is normal 1
- The relationship between serum creatinine and GFR follows a hyperbolic curve, not a linear one, meaning significant kidney function can be lost before serum creatinine rises above normal 2, 3
Potential Pitfalls
- Serum creatinine is affected by non-GFR factors including muscle mass, diet, and exercise 2, 4
- Creatine supplements can artificially elevate serum creatinine and decrease eGFR calculations 4, 5
- For patients with unusual body composition (very muscular or cachectic), measured GFR using exogenous filtration markers may be more accurate 2, 6
This patient's eGFR indicates normal kidney function, and no specific kidney-related interventions are required based on this value alone.