Calculation of eGFR for a 45-Year-Old Patient with Serum Creatinine 0.92 mg/dL and Weight 54 kg
The estimated glomerular filtration rate (eGFR) for this patient is approximately 87 mL/min/1.73 m² using the MDRD formula, indicating normal to mildly reduced kidney function.
Calculation Methods
There are several validated methods to calculate eGFR from serum creatinine. Let's calculate using the most recommended formulas:
1. MDRD (Modification of Diet in Renal Disease) Formula
The MDRD formula is widely recommended by guidelines for estimating GFR 1:
eGFR (mL/min/1.73 m²) = 175 × (serum creatinine [mg/dL])^-1.154 × (age [years])^-0.203 × (0.742 if female)Assuming the patient is female (since sex was not specified):
- eGFR = 175 × (0.92)^-1.154 × (45)^-0.203 × 0.742
- eGFR ≈ 87 mL/min/1.73 m²
If the patient is male:
- eGFR = 175 × (0.92)^-1.154 × (45)^-0.203
- eGFR ≈ 117 mL/min/1.73 m²
2. Cockcroft-Gault Formula
The Cockcroft-Gault formula estimates creatinine clearance and incorporates weight 1, 2:
CrCl (mL/min) = [(140 - age) × weight (kg) × (0.85 if female)] / [72 × serum creatinine (mg/dL)]Assuming the patient is female:
- CrCl = [(140 - 45) × 54 × 0.85] / [72 × 0.92]
- CrCl ≈ 66 mL/min
If the patient is male:
- CrCl = [(140 - 45) × 54] / [72 × 0.92]
- CrCl ≈ 78 mL/min
Interpretation of Results
Clinical Significance
MDRD Result: 87 mL/min/1.73 m² (assuming female) or 117 mL/min/1.73 m² (assuming male)
- This corresponds to CKD Stage 1 (≥90 mL/min/1.73 m²) or Stage 2 (60-89 mL/min/1.73 m²) 2
- Indicates normal to mildly reduced kidney function
Cockcroft-Gault Result: 66 mL/min (assuming female) or 78 mL/min (assuming male)
- This is not normalized to body surface area
- Suggests mildly reduced kidney function
Important Considerations
- The MDRD formula is generally preferred for eGFR reporting as it's been validated in diverse populations 1, 2
- Cockcroft-Gault tends to overestimate GFR in CKD stages 3-5 but is still commonly used for medication dosing 1
- Serum creatinine alone is an inadequate measure of kidney function as it's affected by muscle mass, age, sex, and diet 1, 2
Clinical Implications
- With an eGFR of approximately 87 mL/min/1.73 m² (assuming female), this patient has mild reduction in filtering power (Stage 2 CKD if other evidence of kidney damage exists) 2
- At this level of kidney function, the patient should:
- Be monitored for risk factors for kidney disease progression
- Have blood pressure carefully managed if hypertensive 1
- Have any nephrotoxic medications used with caution
Common Pitfalls to Avoid
- Don't rely solely on serum creatinine to assess kidney function, as it can significantly overestimate GFR 2
- Remember that creatinine production varies with muscle mass, so eGFR may be less accurate in patients with very low or high muscle mass 2
- Consider that the relationship between GFR and serum creatinine is hyperbolic, not linear - significant kidney function can be lost before creatinine rises above normal range 2
For the most accurate assessment of kidney function, consider confirmatory testing with cystatin C in situations where creatinine-based estimates may be less reliable 1, 3.