Time for a change?

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This month’s issue of NDT has an interesting debate concerning whether or not clinical laboratories should start reporting CKD-EPI GFR instead of MDRD. The pro side is here while the con side is here. Basically, the argument for changing is that there is less bias in the CKD-EPI equation, it is more accurate at higher GFRs and more accurately classifies patients as stage 3 as opposed to stage 2 (in terms of overall prognosis). The counter-argument is that, although there is a slight decrease in bias associated with the use of CKD-EPI, it is not any more precise than MDRD – this is more a fault of creatinine as a test of renal function rather than a specific problem with the equations. It should also be mentioned that the CKD-EPI equation is not necessarily better in all circumstances – as documented by Leo in this post about renal transplant recipients.

To (perhaps) settle the argument on one side, the moderator of the debate wrote a commentary and came down on the side of changing to the CKD-EPI equation. The argument is that, even if the improvement is slight, we, as a nephrology community, should not settle for something that is clearly inferior in most circumstances. MDRD was developed in a population of patients with CKD and therefore does not accurately reflect GFR in healthy populations. For this reason, in the research community, there has been a move towards more use of CKD-EPI in the recent past as it is more appropriate for epidemiologic research. The switch to CKD-EPI would not require the use of any new analytes – a simple change in coding in the computers reporting results. In fact, a number of organizations have already switched.

Two other things to mention. Neither equation has been properly validated in Asian populations and this needs to be remedied. Secondly, the role for cystatin C-based or combination equations is still uncertain. Cystatin C is a better predictor of outcomes than creatinine but there are many non-GFR determinants of cystatin C that are likely biasing this and are not related to renal function. Also, the cystatin C test is expensive and has not been fully standardized. There may be a place for the combination equation in patients with borderline GFRs (45-60) in whom the diagnosis of CKD is uncertain.

2 comments

  1. True, but the Epi data are clear. Even in elderly patients, an eGFR of <60 is associated with increased risk. Maybe this is where cystatin c can be of some value. Also, this is an argument for using CKD-Epi because it has less bias.

  2. The problem with these equation is that the margin of error is beyond 30% plus minus (see http://nkdep.nih.gov/lab-evaluation/gfr/estimating.shtml#goto-3 Figure 1) so patients with an eGFR of 60-70 get referred to the renal clinic and are worried that they have kidney disease just because their creatinine is on the upper limit of normal.

    This creates a huge amount of unnecessary renal referrals and patient worries.

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