What is the estimated glomerular filtration rate (eGFR) for a 45-year-old male patient with a serum creatinine level of 1.4 mg/dL and a weight of approximately 50 kilograms?

Calculating eGFR for a 45-Year-Old Male with Creatinine 1.4 mg/dL and Weight 50 kg

For this 45-year-old male patient with serum creatinine 1.4 mg/dL and weight 50 kg, the estimated GFR is approximately 55-60 mL/min/1.73 m² using the MDRD equation, indicating Stage 3a chronic kidney disease with moderately reduced kidney function. 1

Calculation Method Selection

The MDRD equation is the recommended formula for estimating GFR in adults with suspected kidney disease, as it requires only age, gender, race, and serum creatinine without needing body weight 2. This is particularly advantageous for this patient with low body weight (50 kg), as the Cockcroft-Gault formula would be less reliable in underweight individuals 1.

MDRD Equation Calculation

Using the MDRD formula: eGFR = 175 × (serum creatinine)^-1.154 × (age)^-0.203 3

For this patient:

• eGFR = 175 × (1.4)^-1.154 × (45)^-0.203
• eGFR ≈ 58 mL/min/1.73 m² 1

Alternative: Cockcroft-Gault Calculation

If using Cockcroft-Gault (which incorporates weight): [(140 - 45) × 50] / [72 × 1.4] = 47 mL/min (not normalized to body surface area) 3. However, the Cockcroft-Gault formula overestimates creatinine clearance in CKD stage 3-5 and is less accurate than MDRD for this purpose 2.

Clinical Interpretation

This eGFR of approximately 58 mL/min/1.73 m² places the patient at the threshold of Stage 3a CKD (45-59 mL/min/1.73 m²), representing loss of approximately half of normal adult kidney function 1, 3. A GFR below 60 mL/min/1.73 m² is associated with increased prevalence of CKD complications and cardiovascular risk 1.

Immediate Clinical Actions Required

• Confirm this finding with a repeat creatinine measurement in 3-6 months, as factors like recent exercise, infection, fever, or marked hyperglycemia can transiently elevate creatinine independent of true kidney damage 3
• Assess for albuminuria using urine albumin-to-creatinine ratio to complete CKD staging and risk stratification 3
• Consider drug dosage adjustments for renally excreted medications when eGFR is below 60 mL/min/1.73 m² 1

Critical Caveats for This Patient

The low body weight (50 kg) in this patient warrants special consideration, as reduced muscle mass can lead to lower creatinine production, potentially causing the MDRD equation to overestimate true GFR 3. Serum creatinine alone should never be used to assess kidney function because it is affected by creatinine generation, muscle mass, secretion, and extrarenal excretion beyond just GFR 1.

Important pitfall: If this patient is using creatine-containing dietary supplements, these can artificially elevate serum creatinine levels and falsely lower the calculated eGFR 4. A thorough supplement history is essential.

MDRD Limitations in This Case

The MDRD equation has not been validated in persons with normal kidney function or those with severe comorbid conditions, and it systematically underestimates measured GFR at higher values 1. Given this patient's borderline eGFR near 60 mL/min/1.73 m², the true GFR could be slightly higher than calculated 5.

Follow-Up Recommendations

For an eGFR of 58 mL/min/1.73 m², recommend monitoring visits 2-3 times per year with periodic creatinine and potassium measurements 3. Nephrology referral should be considered if eGFR declines below 30 mL/min/1.73 m² or if there is evidence of significant proteinuria 3.