New insights in glomerular filtration rate formulas and chronic kidney disease classification.
BACKGROUND
The MDRD Study equation is the most popular equation for estimating the glomerular filtration rate (eGFR) from serum creatinine (Scr), age, sex and race. Many articles deal with ethnic factors, correcting the MDRD Study equation for different populations, with more or less success. The new CKD-EPI equation introduced the concept of a population-normalized Scr in the eGFR equation for white men (Scr/0.90) and white women (Scr/0.70).


METHODS
We introduce alternative mathematical forms for the MDRD Study equation and the CKD-EPI equation, using the concept of a population-normalized Scr, resulting in a more general and mathematically less complicated form for the eGFR equation.


RESULTS
We show that the normalization constant corresponds to the mean Scr-value for the specific healthy population. We compared the established equations with the new alternative forms, and show that the differences are minimal. The sex/race dependency is completely comprehended in the normalization constant, making the alternative eGFR equations independent of sex and race.


CONCLUSIONS
The age-dependency of eGFR remains and consequently age-dependent cutoff values for the classification of Chronic Kidney Disease (CKD) look more appropriate, contrary to the current classification rules. The population-normalized Scr which is independent of age, sex and race may serve as an alternative for the classification of CKD.
Pottel
Hans
H
Interdisciplinary Research Center, Katholieke Universiteit Leuven Campus Kortrijk, Etienne Sabbelaan 53, B-8500 Kortrijk, Belgium. hans.pottel@kuleuven-kortrijk.be
Hoste
Liesbeth
L
Martens
Frank
F
D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007676:Kidney Failure, Chronic / Q000145:classification* / Q000503:physiopathology; D008297:Male