What is the superior test for estimating glomerular filtration rate (eGFR)?

From the Guidelines

The CKD-EPI equation is the superior test for estimating creatinine filtration rate (eCFR) due to its accuracy and minimal bias in patients with cancer, as demonstrated by a large study by Janowitz et al. 1. This equation has been shown to be the most accurate and least biased estimator of GFR in patients with cancer, based on comparison with radioisotopic clearance with chromium-51 ethylenediamine tetraacetic acid. The use of the CKD-EPI equation is recommended for dosing chemotherapeutic agents in patients with chronic kidney disease (CKD) because it provides a more accurate estimate of GFR compared to other equations like the Cockcroft-Gault formula or the Modification of Diet in Renal Disease study equation. Some key points to consider when using the CKD-EPI equation include:

• It incorporates serum creatinine, age, sex, and race to estimate GFR
• It is more accurate than other equations, particularly in the higher range of GFR (>60 mL/min/1.73m²)
• It is recommended for use in patients with cancer and CKD
• Direct GFR measurement using exogenous filtration markers like iohexol or inulin clearance may be necessary in certain clinical scenarios, such as when more precise measurement is required. The CKD-EPI equation is also supported by other studies, such as the one published in the Journal of Clinical Oncology in 2017, which highlights the importance of accurate GFR estimation in patients with small renal masses 1. However, the most recent and highest quality study, published in Kidney International in 2020, confirms the superiority of the CKD-EPI equation in patients with cancer 1.

From the Research

Estimating Glomerular Filtration Rate (GFR)

The estimation of GFR is crucial for diagnosing and managing chronic kidney disease (CKD) and acute kidney injury (AKI). Several equations have been developed to estimate GFR, including the Cockcroft-Gault (CG) and Modification of Diet in Renal Disease (MDRD) formulas.

Comparison of GFR Estimating Equations

• The CG and MDRD formulas have been compared to measured GFR (mGFR) by renal inulin clearance in several studies 2.
• The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation has been shown to be more accurate than the MDRD equation for estimating GFR, particularly at higher GFR levels 3, 4.
• The CKD-EPI creatinine-cystatin C equation has been found to be superior to conventional equations for estimating GFR in patients with cirrhosis 3.
• However, the diagnostic performance of the CKD-EPI equation has been found to be substantially worse in patients with cirrhosis compared to those without cirrhosis 3.

Limitations of GFR Estimating Equations

• The CG and MDRD formulas have been found to have limitations for proper GFR estimation and CKD classification by GFR levels alone 2.
• The CKD-EPI equation has been found to be inaccurate in estimating point GFR or GFR decline over time in adults with diabetes 5.
• The lack of consistency in the methods and processes of evaluating the diagnostic performance of GFR estimating equations limits reliable quantitative assessment 5.

Superior Test for eGFR

• The CKD-EPI equation is considered a more generalizable and accurate equation for estimating GFR compared to the MDRD equation 4.
• The CKD-EPI creatinine-cystatin C equation has been found to be superior to conventional equations for estimating GFR in patients with cirrhosis 3.
• However, the choice of GFR estimating equation depends on the specific population and clinical context, and further research is needed to determine the most accurate equation for different patient groups 6, 2, 3, 5, 4.