AKI in the ICU

Estimating GFR

All commonly used equations for estimating GFR in the ICU are unacceptably precise and biased toward overestimating GFR.

muscle mass, age, gender, and race all effect concentration
underfeeding, bedrest, and hyper catabolism would all be expected to change creatinine generation
even beyond creatinine kinetics, fluid resuscitation would be expected to change creatinine by changing it's volume of distribution (same with muscle loss during a long hospitalization)
steady state equations (e.g. C-G, CKD-EPI) assume stable sCr, which is often not the case in the ICU.