What does a Glomerular Filtration Rate (GFR) of 228 indicate?

Understanding an Extremely High GFR Value of 228

A glomerular filtration rate (GFR) of 228 ml/min/1.73m² is physiologically implausible in normal clinical settings and likely represents either a measurement error or a specific clinical scenario requiring further investigation.

Possible Explanations for an Abnormally High GFR

1. Measurement or Calculation Errors

• Laboratory error: The most common explanation for such an abnormally high value
• Incorrect data entry: Height, weight, or creatinine values may have been entered incorrectly into estimation equations
• Inappropriate formula selection: Using pediatric formulas for adults or vice versa
• Analytical interference: Substances that interfere with creatinine measurement

2. Creatinine-Related Factors

• Extremely low serum creatinine: Can occur in:

  • Severe muscle wasting conditions
  • Malnutrition
  • Advanced age with sarcopenia
  • Liver disease with reduced creatine production 1
  • Amputation

• Method of creatinine measurement:

  • The Jaffe method overestimates creatinine by 5-15% compared to enzymatic methods 1
  • Different laboratory methods can yield significantly different results

3. Physiological Hyperfiltration States

• Pregnancy: GFR can increase by 40-50% during pregnancy
• High protein diet: Can temporarily increase GFR 2
• Early diabetes: Hyperfiltration can occur before diabetic nephropathy develops
• Obesity: Associated with hyperfiltration, though rarely to this extreme 2

Appropriate Next Steps

1. Verify the measurement:

   • Repeat the test using the same method
   • Check if the correct patient demographics were used in calculations

2. Consider alternative GFR assessment methods:

   • Use combined creatinine and cystatin C-based estimation (eGFRcr-cys) 1, 3
   • Consider direct measurement of GFR using exogenous markers if critical for clinical decision-making 3

3. Clinical context assessment:

   • Evaluate for conditions that might affect creatinine production or secretion
   • Review medication list for drugs that interfere with creatinine measurement or secretion

Interpretation Guidelines

According to KDIGO guidelines, normal GFR in young adults is approximately 125 ml/min/1.73m² 1. Values significantly above this range (>150-160 ml/min/1.73m²) should raise suspicion of measurement error or specific clinical conditions.

The highest physiologically plausible GFR values might be seen in:

• Young, muscular adults
• Pregnant women
• Individuals with early diabetes showing hyperfiltration

However, a value of 228 ml/min/1.73m² exceeds what would be expected even in these scenarios and should prompt immediate verification.

Important Considerations

• Estimation equations have limitations: All GFR estimation equations have reduced accuracy at extremes of GFR values 3, 4
• Non-GFR determinants: Both creatinine and cystatin C are affected by factors unrelated to kidney function 1
• Method standardization: Different laboratories may use different methods for creatinine measurement, affecting results 1

In conclusion, a GFR of 228 ml/min/1.73m² is almost certainly erroneous and requires verification before any clinical decisions are made based on this value.