Shortcomings of the current standard of kidney care
18. Mar 2021 |
7 min read
The problem with eGFR equations that rely on race as a surrogate for muscle mass
Estimated glomerular filtration rate (eGFR) is the primary diagnostic parameter used to detect and manage kidney disease. The current standard of care is to use serum concentrations of creatinine, a by-product of muscle metabolism, to calculate eGFR1. This means that the equations that use creatinine to estimate glomerular filtration rate must be adjusted for a patient’s muscle mass2.
Traditionally, this has been achieved by using race as a surrogate for muscle mass, because previous studies have claimed inherent differences in body composition between blacks and whites3. While those who have grown accustomed to using creatinine over the past few decades have suggested simply removing the race adjustment factor from the aforementioned equations, it is unclear what the implications of such a move would have on eGFR accuracy and clinical decision making.
A new chapter for kidney care in America
In the US there have recently been discussions about the race component of creatine equations. A disproportionate number of the 37 million Americans that have kidney disease are African Americans, Latinos, American Indians, Asian Americans, or Pacific Islanders4. The use of race in clinical algorithms used to detect and manage kidney disease in these groups have contributed to major kidney-health disparities.
“Race modifiers should not be included in equations that estimate kidney function.”
“Current race-based equations should be replaced by a suitable approach that is accurate, inclusive, and standardized in every laboratory in the US.”
The hope is that clinical implementation of equations that provide an unbiased assessment of kidney function would allow health professionals to ensure equitable outcomes in all patients with kidney disease.
Cystatin C based eGFR is independent of muscle mass and race
Fortunately, there is an alternative biomarker that is already being used in many hospitals around the world. Cystatin C is ubiquitously expressed through all nucleated cells1. Individuals with similar kidney function can therefore be expected to have similar serum concentrations of cystatin C. This means that equations used for calculating GFR do not depend on an individual’s muscle mass or race.
Consequently, cystatin C is also considered the preferred marker for eGFR in patient groups with significant variability in muscle mass:
Patients with spinal cord injuries8
Patients with conditions linked to malnutrition7
Clinical adoption of cystatin C may well present the opportunity to “replace current race-based equations with a suitable approach that is precise, inclusive and standardized in every laboratory in the United States.”4
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