What is the estimated glomerular filtration rate (eGFR) for a 70-year-old male with a serum creatinine (Cr) level of 1 and a weight of 58 kilograms (kg)?

Estimated Glomerular Filtration Rate (eGFR) Calculation for a 70-Year-Old Male

For a 70-year-old male with serum creatinine of 1 mg/dL and weight of 58 kg, the estimated glomerular filtration rate (eGFR) is 56.4 mL/min using the Cockcroft-Gault formula, which is the most appropriate formula for this clinical scenario. 1

Calculation Using Cockcroft-Gault Formula

The Cockcroft-Gault formula is calculated as follows:

• eGFR (mL/min) = [(140 - age) × weight] / [72 × SCr] 1
• eGFR = [(140 - 70) × 58] / [72 × 1]
• eGFR = [70 × 58] / 72
• eGFR = 4060 / 72
• eGFR = 56.4 mL/min

Rationale for Using Cockcroft-Gault

• The Cockcroft-Gault formula is widely used in clinical practice for estimating renal function, particularly when considering medication dosing 1, 2
• It incorporates important variables that affect renal function: age, weight, gender, and serum creatinine 1
• For elderly patients, the Cockcroft-Gault formula has been used as a standard measure to screen for renal failure 1

Alternative Formulas and Considerations

MDRD Formula

• The MDRD formula estimates GFR as: 186 × [SCr (mg/dL)]^-1.154 × [age (years)]^-0.203 × [0.742 if female] × [1.21 if African American] 1
• This would yield a different result but is normalized to body surface area (mL/min/1.73 m²) 1
• MDRD tends to overestimate GFR compared to Cockcroft-Gault in elderly patients 3

CKD-EPI Formula

• More accurate than MDRD, especially at higher GFR values 4
• However, for elderly patients (>70 years), specialized formulas may be more appropriate 5

BIS1 and FAS Formulas

• Recent research suggests that for patients over 70 years old, the BIS1 (Berlin Initiative Study) formula may be more accurate 5
• These specialized formulas tend to estimate lower eGFR values in elderly patients compared to CKD-EPI and MDRD 5

Clinical Implications of the eGFR Result

• An eGFR of 56.4 mL/min indicates moderate reduction in kidney function (Stage 3a CKD) 1
• This level of renal function requires:
  • Careful medication dosing for renally cleared drugs 2
  • Monitoring for further decline in renal function 1
  • Consideration of nephrotoxic medication avoidance 1

Common Pitfalls in eGFR Estimation

• Serum creatinine alone is an inadequate measure of renal function, especially in elderly patients 1
• The Cockcroft-Gault formula may underestimate GFR for normal and moderately reduced levels of renal function 1
• Different laboratory methods for measuring serum creatinine (Jaffe vs. enzymatic PAP) can affect the accuracy of eGFR calculations 1
• For patients with significantly impaired renal function, the Cockcroft-Gault formula may overestimate renal function 1

Practical Recommendations

• Use the calculated eGFR of 56.4 mL/min for medication dosing decisions 2
• Consider that this patient has moderate renal impairment despite a "normal" serum creatinine level 1
• For elderly patients, it is particularly important to calculate eGFR rather than relying on serum creatinine alone 1
• Regular monitoring of renal function is recommended, especially if prescribing potentially nephrotoxic medications 1