Contrarian Viewpoint Re: 'Further Efforts to Refine Glomerular Filtration Rate Estimation Should Continue'
Of course, none of this is to deny that it is useful to define GFR with some precision and accuracy. Certainly, it is a key parameter. The question is not whether further incremental gain will be made by continuing this line of investigation (the answer undoubtedly will be yes) but whether equivalent time and effort spent instead on pursuing other research would ultimately yield greater benefits to patients. In other words, this is an opportunity cost consideration.
We have become much more sophisticated in estimating GFR in the 14 years since the landmark publication introducing the MDRD study equation in 1999. But major advances in renoprotective strategies have not emerged over the same time period. Nephrology has remained the internal medical subspecialty with the smallest number of randomized controlled trials. The trials that have been performed (with erythropoiesis-stimulating agents or bardoxolone for example) have not yielded the breakthroughs that many had hoped for. Certainly, awareness of CKD has improved, and this has influenced referral practices. But it has not been easy to show that this translates into better patient outcomes. In the next dozen years, would more efforts by nephrology investigators devoted instead to interventional or observational studies of therapeutics be a more fruitful pursuit?
Refining our ability to better discern changes in a given person's kidney function over time is more important than estimating that person's static GFR value with greater and greater precision and accuracy. Changes in renal function trajectory will directly influence clinical decisions regarding delivering renoprotective therapies or withholding potentially nephrotoxic interventions. Interventional trials may become more efficient. Numerous factors that account for substantial between-person differences in the relation between filtration marker and GFR levels (e.g. sex or race/ethnicity) do not vary within person over time. So filtration markers which may not discriminate renal function well between individuals may do fine in tracking change over time for that individual. The emphasis on longitudinal vs. cross-sectional analyses will thus represent a shift in research focus and methodology.