CKD Staging: CKD-EPI Equation May Overclassify Severity

The way chronic kidney disease (CKD) is staged – how severe it’s considered to be – can vary depending on the equation doctors apply to estimate a key measure of kidney function. A recent observation, reported by Medscape News UK, highlights that the CKD Epidemiology Collaboration (CKD-EPI) equation tends to classify a higher proportion of patients as having more advanced stages of CKD compared to other methods.

Understanding Kidney Disease Staging and eGFR

Chronic kidney disease isn’t a single condition; it’s a spectrum of damage to the kidneys. Staging helps doctors understand the severity of the disease, guide treatment decisions, and predict potential outcomes. This staging relies heavily on the estimated glomerular filtration rate, or eGFR. The eGFR measures how well your kidneys are filtering waste from your blood. A lower eGFR indicates poorer kidney function.

Traditionally, the Modification of Diet in Renal Disease (MDRD) Study equation was widely used to estimate eGFR. However, research has suggested that the CKD-EPI equation may be more accurate, particularly in identifying individuals with CKD. Medscape reported on this earlier research, noting the CKD-EPI equation’s potential to outperform the MDRD equation.

The Shift Towards Race-Free Equations

For years, equations used to calculate eGFR included a race-based component, which has been a source of controversy and contributed to health disparities. Recognizing this, the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) convened a Task Force to develop a race-free approach. The result was the 2021 CKD-EPI equation, which is now recommended for use. The final report, published in Health Equity in January 2024, detailed the implementation of this fresh equation, utilizing both creatinine and cystatin C testing for a more comprehensive assessment.

What Does This Mean for Patients?

The difference in staging between equations isn’t necessarily about a change in a patient’s underlying kidney function. It’s about how that function is interpreted. If a patient is staged higher with the CKD-EPI equation, it doesn’t automatically mean their kidneys are suddenly worse. It means they may be identified as needing closer monitoring or earlier intervention based on the new classification. This is particularly relevant as the CKD-EPI equation is designed to be more sensitive to subtle changes in kidney function.

It’s important to remember that eGFR is an estimate, not a perfect measurement. Several factors can influence it, including age, sex, muscle mass, diet, and certain medications. A single eGFR result shouldn’t be viewed in isolation; doctors consider trends over time and other clinical information to secure a complete picture of a patient’s kidney health.

Implications for Primary Care

The shift to the CKD-EPI equation has particular implications for primary care physicians, who often are the first point of contact for patients with early-stage CKD. Because the CKD-EPI equation may identify more patients with advanced stages, primary care doctors may see an increase in the number of patients they need to refer to nephrologists (kidney specialists). This could strain resources and require adjustments to referral pathways.

the change in staging could affect how certain medications are prescribed. Some medications have dosage adjustments based on eGFR, so a higher stage could lead to different prescribing practices. However, it’s crucial that these decisions are made on a case-by-case basis, considering the individual patient’s overall health and needs.

Understanding the Nuances of eGFR Equations

The development of eGFR equations is an ongoing process. Researchers continually refine these equations to improve their accuracy and address limitations. The inclusion of cystatin C alongside creatinine in the 2021 CKD-EPI equation represents a significant step forward. Creatinine is a waste product produced by muscle metabolism, even as cystatin C is produced by all nucleated cells. Cystatin C is less affected by muscle mass than creatinine, making it a potentially more accurate marker of kidney function, especially in individuals with unusual body compositions.

However, it’s important to acknowledge that even the most advanced eGFR equations aren’t foolproof. They are based on population-level data and may not perfectly reflect the kidney function of every individual. There’s inherent uncertainty in any estimated measurement, and clinical judgment remains paramount.

What Comes Next: Ongoing Evaluation and Refinement

The implementation of the 2021 CKD-EPI equation is not the complete of the story. The NKF and ASN Task Force will continue to monitor its performance and gather data on its impact on patient care. Ongoing research will focus on further refining the equation and identifying additional biomarkers that could improve its accuracy. Regular reviews of clinical guidelines will ensure that healthcare professionals have the most up-to-date information on CKD diagnosis and management. The goal is to provide the best possible care for individuals at risk of or living with chronic kidney disease, and to address the health disparities that have historically plagued this field.