How Cystatin C measurement contributes to health care equity

Kidney function is assessed in the laboratory by measuring serum creatinine (Cr) and/or Cystatin C (CysC) and estimating glomerular filtration rate (GFR) using equations. Since 2009 the most frequently used equation has been the 2009 CKD-EPI equation, which includes Cr, age, sex and race in the equation (eGFRcr). This has resulted in higher eGFRs for individuals who are identified as Black compared with non-Blacks, and has been linked to disparities in care, including delays in the diagnosis of kidney disease and eligibility for kidney transplantation.

 

Race is viewed as a social construct, which ignores diversity within and among racial groups, and including race in GFR estimating equations may contribute to systemic racism in medicine. The National Kidney Foundation and the American Society of Nephrology (NKF-ASN) has re-assessed the inclusion of race in the estimation of GFR in the US and its implications for diagnosis and patient management. As a result, they have refitted the CKD-EPI equation without the race variable and recommended the immediate implementation of the 2021 CKD-EPI equation. Their second recommendation was to facilitate the increased, routine and timely use of CysC. CysC is non-glycosylated protein that is produced by all nucleated cells and is freely filtered by the glomerulus.  It appears to be less affected by age, sex, muscle mass, diet and race than Cr. The current CysC-based equation for eGFR (eGFRcys) does not include race, but has similar accuracy as the 2009 eGFRcr, therefore no refit was needed. The 2009 eGFRcr-cys equation (that uses both Cr and CysC measurements), however, has also been refitted to not include race, and currently provides the most accurate GFR estimation among the various equations.

 

Offering CysC in the laboratory therefore may facilitate racial bias-free kidney function assessment and increase the accuracy of eGFR.

 

 

At the conclusion of this session, the participant will be able to: