Should Past eGFRcr Readings Be Updated for the New 2021 Calculation?
No, past eGFRcr readings should not be routinely recalculated using the 2021 race-free CKD-EPI equation, but all future eGFR calculations must use the 2021 equation going forward. 1, 2
Rationale for Not Updating Historical Values
The primary focus should be on implementing the 2021 CKD-EPI equation prospectively rather than retrospectively recalculating historical eGFR values. 2 The National Kidney Foundation Laboratory Engagement Working Group specifically recommends immediately replacing older eGFR equations (MDRD Study and CKD-EPI 2009) with the new CKD-EPI 2021 equation for all current and future calculations. 2
Key Considerations Against Retrospective Recalculation
Clinical decision-making was based on the equation available at the time of measurement, and those decisions were appropriate given the standards of that era. 1
The 2021 equation produces eGFR values that are on average 2.7 mL/min/1.73 m² higher than the 2009 equation, with greater variation among males. 3 Retrospectively changing historical values could create confusion about disease progression trajectories and whether changes represent true clinical change versus calculation methodology differences.
Approximately 17% of patients are reclassified to a higher eGFR category when switching from the 2009 to 2021 equation, with the highest proportion (28%) reclassified from G5 to G4. 3 This reclassification reflects improved accuracy rather than actual changes in kidney function at those historical time points.
Mandatory Prospective Implementation
All clinical laboratories must immediately implement the race-free 2021 CKD-EPI equations for current eGFR reporting. 1, 2
Implementation Standards
The KDOQI Work Group supports the use of the race-free 2021 CKD-EPI eGFRcr, 2021 CKD-EPI eGFRcr-cys, and the 2012 CKD-EPI eGFRcys equations for adults. 1
These approaches do not include race as a variable in computing or reporting of eGFR and align with the NKF-ASN Task Force recommendations on use of race in diagnosis of kidney disease. 1
Use of race in the computation of eGFR should be avoided. 1
Use the same equation within geographical regions (as defined locally) and as large as possible. 1
Clinical Implications for Longitudinal Monitoring
Interpreting Trends Across the Equation Change
When reviewing a patient's eGFR trend that spans the transition from 2009 to 2021 equations:
Document clearly in the medical record which equation was used for each historical measurement. 2 This prevents misinterpretation of apparent "improvements" in kidney function that are actually due to equation changes.
Expect an apparent increase in eGFR of approximately 2-3 mL/min/1.73 m² when transitioning to the 2021 equation, particularly in male patients. 3 This should not be interpreted as clinical improvement.
The risk of progressing to kidney failure was 22% less among patients reclassified to higher eGFR categories (adjusted subdistribution HR 0.78,95% CI 0.65-0.94), suggesting the 2021 equation provides more accurate risk stratification. 3
Validation in Special Populations
Among kidney transplant recipients, the 2021 race-free CKD-EPI equations perform similarly to previous CKD-EPI equations that included race correction terms. 4 The 2021 equations demonstrated similar median bias, precision, and accuracy compared to measured GFR. 4
The Kidney Failure Risk Equation (KFRE) remains accurate and well-calibrated when using the CKD-EPI 2021 eGFR equation, particularly for eGFR <45 mL/min/1.73 m². 5
Common Pitfalls to Avoid
Do not attempt to "correct" or recalculate historical eGFR values in the electronic medical record, as this creates confusion about actual disease progression and may obscure true clinical changes that occurred. 2
Do not assume that an apparent increase in eGFR after implementing the 2021 equation represents clinical improvement—this is expected due to the equation change. 3
Ensure your laboratory has actually implemented the 2021 equation, as a 2019 survey found 23% of laboratories were using incorrect equations not suitable for standardized creatinine measurements. 2
When eGFR is thought to be inaccurate (extremes of muscle mass, body composition, or critical clinical decisions), consider using the combined creatinine-cystatin C equation (eGFRcr-cys) or measured GFR with exogenous markers. 1, 6, 7