What is the recommended approach to estimating kidney function in the 2024 Kidney Disease: Improving Global Outcomes (KDIGO) (Kidney Disease: Improving Global Outcomes) chronic kidney disease (CKD) (Chronic Kidney Disease) guidelines?

Recommended Approach to Estimating Kidney Function in the 2024 KDIGO CKD Guidelines

According to the 2024 KDIGO guidelines, equations that provide an estimate of the glomerular filtration rate (GFR) are more accurate for determining kidney filtration and are preferred over equations that rely on serum filtration markers alone. 1

Initial Assessment of Kidney Function

• The recommended approach follows a stepwise algorithm:
  1. Use serum creatinine (SCr) and creatinine-based estimated GFR (eGFRcr) as the initial test for GFR assessment 1
  2. Consider potential sources of error in eGFRcr and determine if more accurate assessment is needed
  3. If eGFRcr is expected to be inaccurate or if GFR affects important clinical decisions, measure cystatin C and use combined creatinine and cystatin C-based eGFR (eGFRcr-cys) 1
  4. If even greater accuracy is needed, measure GFR directly using exogenous filtration markers 1

When to Use Combined Creatinine and Cystatin C-Based eGFR

• eGFRcr-cys is specifically recommended in clinical situations when:
  • eGFRcr is likely to be inaccurate (e.g., extremes of muscle mass, diet)
  • GFR affects critical clinical decision-making (e.g., drug dosing, diagnosis/staging of CKD) 1, 2
  • There are discrepancies between clinical presentation and eGFRcr

Special Considerations

• Race in GFR estimation: The guidelines explicitly state that use of race in computation of eGFR should be avoided 1
• Cystatin C is not routinely needed: The guidelines do not recommend measuring cystatin C in all patients, but rather in specific clinical scenarios when more accurate GFR assessment is required 1
• Laboratory standardization: The guidelines emphasize the importance of using validated equations and standardized laboratory methods for measuring filtration markers 1

Advantages of GFR Estimating Equations

• GFR estimating equations incorporate multiple variables that affect serum filtration marker levels beyond GFR
• These equations provide more accurate assessment of kidney function than serum creatinine or cystatin C alone 1
• The combined creatinine and cystatin C-based equation (eGFRcr-cys) compensates for limitations of individual markers, demonstrating superior performance across populations 2

Common Pitfalls to Avoid

• Do not rely solely on serum filtration markers: Using serum creatinine or cystatin C alone without an estimating equation is explicitly discouraged 1
• Do not assume a single abnormal eGFR indicates CKD: Confirmation of chronicity (≥3 months) is required for CKD diagnosis 1
• Do not use outdated equations: The Cockcroft-Gault equation includes a race variable that is no longer recommended in clinical practice 1
• Do not assume standardization across all laboratories: While standardized approaches are recommended, implementation may vary 1

The 2024 KDIGO guidelines provide a clear, evidence-based approach to GFR estimation that prioritizes accuracy while recognizing practical clinical considerations and the need for standardization across healthcare systems.