How to compute eGFR for a 93-year-old male patient with impaired renal function?

eGFR Calculation for a 93-Year-Old Male with Serum Creatinine 96 mg/dL

For a 93-year-old male with serum creatinine 96 mg/dL (0.96 mg/dL), use the CKD-EPI equation to calculate eGFR, which yields approximately 75-80 mL/min/1.73 m² depending on race, representing normal to mildly decreased kidney function for this age. 1, 2

Calculation Method

The CKD-EPI equation is the preferred formula for estimating GFR in clinical practice, as it provides superior accuracy compared to older formulas like MDRD, particularly at GFR values >60 mL/min/1.73 m². 1, 3

CKD-EPI Formula:

• eGFR = 141 × min(SCr/κ, 1)^α × max(SCr/κ, 1)^-1.209 × 0.993^age 1
  • For males: κ = 0.9, α = -0.411 1
  • SCr = serum creatinine in mg/dL (0.96 mg/dL in this case)
  • Age = 93 years

Calculation Steps:

• SCr/κ = 0.96/0.9 = 1.067 1
• min(1.067,1) = 1.0 1
• max(1.067,1) = 1.067 1
• eGFR = 141 × 1.0^-0.411 × 1.067^-1.209 × 0.993^93 1
• eGFR ≈ 75-80 mL/min/1.73 m² 1, 3

Clinical Interpretation

This eGFR represents Stage 2 CKD (GFR 60-89 mL/min/1.73 m²) or normal kidney function for age, as GFR declines by approximately 1% per year after age 40, meaning a 93-year-old would be expected to have lost approximately 50% of peak GFR. 1, 2

Key Clinical Points:

• GFR ≥60 mL/min/1.73 m² does not meet criteria for chronic kidney disease unless albuminuria or other kidney damage markers are present. 3
• Normal GFR for young adults is approximately 130 mL/min/1.73 m² for males, with physiologic decline of 0.75-1% per year starting in the third or fourth decade. 2, 3
• At age 93, an eGFR of 75-80 mL/min/1.73 m² is actually relatively preserved kidney function. 2

Critical Caveats for Elderly Patients

Never use serum creatinine alone to assess kidney function in elderly patients—this significantly underestimates renal insufficiency due to age-related muscle mass loss. 1, 2

Important Limitations:

• The CKD-EPI equation systematically underestimates GFR in the oldest patients, with the discrepancy most pronounced in those >90 years old. 2, 4
• Serum creatinine production decreases with age-related muscle mass loss independently of kidney function, making a "normal" creatinine misleading. 2
• A serum creatinine of 1.2 mg/dL can represent a creatinine clearance of 110 mL/min in a young adult but only 40 mL/min in an elderly patient. 2
• When serum creatinine significantly increases, GFR has already decreased by at least 40%. 2

Alternative Calculation: Cockcroft-Gault (For Medication Dosing)

If this calculation is needed for medication dosing decisions, use the Cockcroft-Gault formula instead, as most drug dosing studies have historically used this equation. 2

Cockcroft-Gault Formula:

• CrCl (mL/min) = [(140 - age) × weight (kg)] / [72 × serum creatinine (mg/dL)] 1, 2
• For a 93-year-old male weighing 70 kg: CrCl = [(140 - 93) × 70] / [72 × 0.96] = 47.6 mL/min 2

Note that Cockcroft-Gault provides non-indexed creatinine clearance (mL/min), not eGFR (mL/min/1.73 m²), and consistently underestimates GFR in elderly patients. 2

Recommendations for Clinical Management

• Assess albuminuria using urine albumin-to-creatinine ratio to complete CKD staging, as eGFR alone is insufficient. 1
• Review all medications for renal appropriateness and dose adjustments, particularly if using Cockcroft-Gault calculation shows CrCl <60 mL/min. 2
• Avoid nephrotoxic medications (NSAIDs, aminoglycosides) and ensure adequate hydration status. 2
• Monitor serum creatinine and potassium levels periodically, with frequency based on clinical stability and medication regimen. 1
• Consider referral to nephrology if eGFR falls below 30 mL/min/1.73 m² or if there is rapidly progressive kidney disease. 1