Management

Estimating GFR: Are We on Target?

AUTHOR:
James Matera, DO
Practicing Nephrologist, Senior Vice President for Medical Affairs, and Chief Medical Officer CentraState Medical Center, Freehold, New Jersey

CITATION:
Matera J. Estimating GFR: are we on target? Consultant360. Published online March 22, 2021.

 

Evaluating a patient’s estimated glomerular filtration rate (eGFR) is a critical part of medicine. Racial disparities in medicine are quickly becoming better known and can lead to unconscious bias in medicine. Race plays a role in the estimates we currently have for evaluation of renal function. In studies, people who are Black have a 16% higher average measured glomerular filtration rate (GFR) compared with people who are not Black and have the same age and sex and similar serum creatinine levels.1 Two recent articles have investigated race, both as it pertains to transplantation and general understanding of renal function.

Zelnick and colleagues3 aimed to compare eGFR with actual measured GFR to examine the association between eGFR calculated with a coefficient for race vs without a coefficient for race, and what it meant for time until eligibility for renal transplantation. Racial disparities in kidney transplantation are well known and continue despite changes in organ procurement in the United States. Patients who are Black are less likely to be referred for, registered for, move up the waiting list for, and finally receive a transplant, despite the knowledge of improved renal outcomes.2 Zelnick and colleagues found that when race is included in the eGFR equation, there is a greater bias in GFR estimation. This directly led to a time delay in listing for renal transplant, further exacerbating the disparities that are already seen.3

Even before race became as important of an issue with eGFR, the concept was still questioned. In 2006, the limitations of current GFR estimates showed to be inaccurate in patients who had chronic kidney disease (CKD) and who did not.4 Physicians had to be educated about using the eGFR calculation in stratifying the levels of chronic kidney disease (CKD).4 

Spring forward to 2021, and authors in the New England Journal of Medicine postulate again;5 this time concerning racial disparities in the eGFR calculations. Most laboratories estimate GFR using race, but there is a trend, especially in academic medical centers, to remove the race coefficient from eGFR measurements. However, no reports have systematically evaluated all options for computing and reporting eGFR. There are “race-free” alternatives available, but there have not been studies to date to compare effectiveness.5

One of these equations uses cystatin C as part of the equation. eGFR serum cystatin C (eGFRcys) is a validated race-free equation with minimal bias. Assays for cystatin C are more widely available but still suffer from delays, lack of some standardization, and do not take into account factors like weight and obesity.5 We expect the National Kidney Foundation and American Society of Nephrology task force to come up with suggestions and evidence-based guidelines on proper calculations for eGFR.

References:

  1. Levey AS, Titan SM, Powe RN, Coresh J, Inker LA. Kidney disease, race, and GFR estimation. Clin J Am Soc Nephrol. 2020;15(8):1203-1212. https://doi.org/10.2215/cjn.12791019
  2. Sood A, Abdullah NM, Abdollah F, et al. Rates of kidney transplantation from living and deceased donors for blacks and whites in the United States, 1998 to 2011. JAMA Intern Med. 2015;175(10):1716-1718. https://doi.org/10.1001/jamainternmed.2015.4530 
  3. Zelnick L, Leca N, Young B, Bansal N. Association of the estimated glomerular filtration rate with vs without a coefficient for race with time to eligibility for kidney transplant.  JAMA Netw Open. 2021;4(1):e2034004. https://doi.org/10.1001/jamanetworkopen.2020.34004 
  4. Stevens LA, Coresh J, Greene T, Levey AS. Assessing kidney function—measured and estimated glomerular filtration rate. N Engl J Med. 2006;354(23):2473-2483. https://doi.org/10.1056/nejmra054415 
  5. Diao JA, Inker LA, Levey AS, Tighiouart H, Powe NR, Manrai AK. In search of a better equation—performance and equity in estimates of kidney function. N Engl J Med.  2021;384(5):396-399. https://doi.org/10.1056/nejmp2028243