Discrepancies in the RIFLE classification are due to the method used to assess the level of derangement of kidney function.

Abstract Purpose We hypothesized that RIFLE based on creatinine clearance (CrCl) is superior to that based on serum creatinine (sCr) or Cockroft-Gault (C-G) because it is an earlier marker of kidney dysfunction. Materials and Methods At day 3 of admission, we compared the RIFLE based on sCr, C-G, and CrCl with 28-day mortality and development of RIFLE-F during intensive care unit stay. Results Percentages in the RIFLE levels were similar for the 3 estimates, but the patients included in each level were different; with CrCl as the reference, κ statistic was 0.29 (95% confidence interval, 0.15-0.43) for sCr and 0.21 (0.07-0.36) for C-G. Mortality at day 28 was 19.3%, with percentages of mortality increasing with RIFLE based in CrCl but not sCr or C-G (area under the curve, 0.57 [45-72] for C-G; 0.57 [44-72] for sCr; and 0.64 [52-79] for CrCl). Logistic regression only showed an independent relationship with mortality for RIFLE measured with CrCl. Conclusions RIFLE classification using sCr or C-G at the third day of admission predicts outcome less accurately than with the use of CrCl. Because of the delay in the rise of sCr after a sudden glomerular filtration rate decrease, RIFLE based in CrCl may represent an advantage in terms of precocity.