Assessing Kidney Function

Key Differences Between Creatinine Clearance and eGFR

• Creatinine clearance measures the volume of blood plasma that is cleared of creatinine per unit time, typically requiring timed urine collection and serum creatinine measurement, as noted by the Kidney International guidelines 1
• eGFR is calculated using equations that incorporate serum creatinine and/or cystatin C along with demographic variables, without requiring urine collection, according to the Kidney International guidelines 1, 2
• eGFR is derived from serum biomarkers using validated equations, such as CKD-EPI and MDRD, as recommended by the Kidney International guidelines 3

Clinical Implications of the Differences

• The Kidney International guidelines recommend eGFR using serum creatinine as the initial test for kidney function assessment in clinical practice, due to its accuracy and convenience 3, 4
• Creatinine clearance is generally not recommended as the first-line method for GFR assessment, as it may be less accurate and more cumbersome, according to the Kidney International guidelines 4
• The Kidney International guidelines suggest using eGFR for routine kidney function assessment, classifying CKD stages, and screening for kidney disease 1, 3, 4

When to Use Each Method

• The Kidney International guidelines recommend considering measured creatinine clearance when eGFR is thought to be inaccurate and measured GFR using exogenous markers is not available, or when evaluating patients with extremes of muscle mass or dietary intake 4, 5, 6
• Measured GFR using exogenous markers is recommended when more accurate assessment of GFR will impact treatment decisions, or when both eGFR and creatinine clearance are likely to be inaccurate, according to the Kidney International guidelines 3, 4

Common Pitfalls and Caveats

• The Kidney International guidelines note that eGFR may be less accurate in certain populations, such as the very elderly or those with extremes of body size, and that different equations may yield different results 3, 6
• Standardization of creatinine assays is critical for accurate eGFR calculation, as emphasized by the Kidney International guidelines 4