The ASN and NKF have a joint task force working toward a response to the race and eGFR problem and they are now inviting people to submit oral and written testimony. I signed up. Hopefully I get an opportunity, but suspect there will be too many people for them to hear even a fraction of the applicants.
I have been thinking about race and eGFR and this is where I am at…
- Race is a social not a biological construct
- People identified as black (or self-identified as black) have higher measured GFR for the same serum creatinine as non-blacks
- These higher eGFR results in black people (self-identified or not), a marginalized group and a population already at increased risk of adverse kidney outcomes, being denied transplant listing and CKD referral.
But what is not ever seem to be questioned in this discussion is the perverse use of estimated GFRs to make critical binary decisions in individual patients. The eGFR equations are amazing how well they predict GFR for groups of patients with minimal bias, but their reliability in an individual is stunningly imprecise. Accuracy in individual patients is measured by P30, the likelihood that the true value will be within 30% of the measured value. The P30 is 84% with CKD-Epi, a bit better compared to the 80% in MDRD. This means that for the critical decision of whether to list a patient for a kidney transplant, a patient with an eGFR of 21 will have an actual measured GFR somewhere between 15 and 27 in 84% of cases. This 30% spread is greater than the 16% adjustment for black race.
Though using race for eGFR should be stopped, and we can do that today by making cystatin-c the coin of the realm, this doesn’t change the problem of over indexing on eGFR for individual patient decisions. Cystatin C is no better than creatinine in providing a precise estimate in eGFR (P30 86%). Decisions like transplant listing and CKD referral should not rely on a measurement with so much uncertainty. We report eGFR on lab reports but give physicians no sense of the imprecision hidden in that number.
I think if eGFR were reported as a range (±30%), we would stop using sharp cut-off limits for critical decisions like transplant and referral.
The use of sharp cutoff for decisions like transplant and CKD referral harms all patients with CKD, not just black people. We should immediately to remove race from eGFR calculations by standardizing cystatin-C as the way to assess eGFR but at the same time we should start the process of unwinding guidelines and individual patient decisions from being wedded to inaccurate estimates of GFR.