Uncritical Use of Estimating Equations

With my doctoral thesis in nephrology and my practice as a family physician, I looked forward to this article on renal failure (1). In my opinion, there is nothing wrong with both the study and the article, except for the uncritical application of creatinine-based renal function estimating equations on all strata of the population. The currently favored Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation from 2009 may have less shortcomings than the Modification of Diet in Renal Disease (MDRD) equation from 1989, but it does not require to specify body weight, while it includes skin color. The algorithm takes darker skin color into account to allow for associated greater muscle mass which correlates with creatinine levels. The Cockroft-Gault equation takes weight into account, but nowadays, it is considered obsolete for more reasons than just its poor validation (developed in 1973 based on data from 249 male subjects). Furthermore, the average person in Mecklenburg may be underrepresented with a reference body surface of 1.73 m². This would be no more than a minor annoyance, medically overcome with ease, if it weren’t for the fact that, due to pharmacovigilance requirements, the glomerular filtration rate has rightfully found its way into clinical routine and the precise representation of renal function has become essential, not only for medicolegal reasons. I think the e(stimated) GFR, based on serum creatinine levels, is not precise enough, especially in heavy and muscular persons, but also in underweight, cachectic patients. In my opinion, an individualized view on renal function, considering further factors (such as build, development over time) would make better sense.