What is the eGFR of a 45-year-old male with impaired renal function (serum creatinine 1.05 mg/dL) and weighing 50 kg?

Calculating eGFR for a 45-Year-Old Male with Serum Creatinine 1.05 mg/dL and Weight 50 kg

The estimated glomerular filtration rate (eGFR) for this 45-year-old male is approximately 67 mL/min using the Cockcroft-Gault formula, which places him in Stage 2 chronic kidney disease (mild reduction in kidney function).

Calculation Method

The Cockcroft-Gault equation is the most appropriate formula to use in this case as it accounts for the patient's actual weight, which is particularly important when the patient's weight differs significantly from average body size 1.

Using the Cockcroft-Gault formula:

• GFR (mL/min) = [(140 - age) × weight (kg)] / [72 × serum creatinine (mg/dL)]
• GFR = [(140 - 45) × 50] / [72 × 1.05]
• GFR = [95 × 50] / [75.6]
• GFR = 4750 / 75.6
• GFR = 62.8 mL/min (approximately 63 mL/min)

Interpretation of Results

According to the National Kidney Foundation guidelines, this eGFR value falls into Stage 2 CKD classification (60-89 mL/min/1.73 m²), indicating a mild decrease in GFR 2, 1.

It's important to note that:

• This patient's eGFR is at the lower end of Stage 2, suggesting early kidney function decline
• The patient's relatively low body weight (50 kg) impacts the calculation and interpretation
• At this level, the patient has a mild reduction in filtering power 1

Clinical Implications

At this level of kidney function:

• The patient does not yet have severe renal impairment, but monitoring is warranted
• The risk of cardiovascular disease begins to increase even at this mild level of kidney dysfunction 2
• Hypertension should be carefully managed if present 2
• Medication dosing may need adjustment for drugs cleared by the kidneys

Alternative Calculation Methods

For comparison, using the MDRD 4-variable equation:

• GFR (mL/min/1.73 m²) = 186 × (SCr)^-1.154 × (age)^-0.203 × (0.742 if female) × (1.21 if Black-American)
• For this 45-year-old male with SCr 1.05 mg/dL (assuming non-Black):
• eGFR ≈ 78 mL/min/1.73 m² 2

Important Considerations

1. Weight consideration: The patient's weight of 50 kg is below average for adult males, which affects the Cockcroft-Gault calculation 2, 1

2. Serum creatinine limitations: Serum creatinine alone is an inadequate measure of kidney function as it's affected by muscle mass, diet, and other factors 2, 1

3. Confirmation needed: A single eGFR calculation should be confirmed with repeat testing within 3 months to establish chronicity before making definitive diagnoses 1

4. Potential confounders: Factors that can affect serum creatinine levels include:

   • Muscle mass (lower muscle mass can lead to lower creatinine despite reduced kidney function)
   • Diet (high protein intake can temporarily affect results)
   • Medications that affect creatinine secretion 3, 4

5. Follow-up recommendations: For a patient with this eGFR level:

   • Monitor kidney function at least annually
   • Evaluate for common causes of CKD such as diabetes and hypertension
   • Consider screening for albuminuria to assess for kidney damage 1