Limited ability of SOFA and MOD scores to discriminate outcome: A prospective evaluation in 1,436 patients

Abstract

Purpose: The multiple organ dysfunction (MOD) score and sequential organ failure assessment (SOFA) score are measures of organ dysfunction and have been validated based on the association of these scores with mortality. We sought to compare the performance of the SOFA and MOD scores in a large cohort of consecutive multisystem intensive care unit (ICU) patients. Methods: Prospective automated daily measurements of MOD and SOFA scores were performed in 1,436 patients admitted to a multisystem ICU in the Calgary Health Region over a one-year period. Logistic regression modeling techniques were used to describe the association of SOFA and MODS with mortality. Receiver operator characteristic (ROC) curves were used to assess the model's discriminatory ability. Results: For ICU and hospital mortality, there was very little practical difference between the SOFA and MOD scores in their ability to discriminate outcome as determined by the area under the ROC. However, compared to previous literature, the discriminatory ability of both scores in this population was weak. As well, the calibration of the models was poor for both scores. The SOFA cardiovascular component score performed better than the MOD cardiovascular component score in the discrimination of both ICU and hospital mortality. Conclusions: SOFA and MOD scores had only a modest ability to discriminate between survivors and non-survivors. These results question the appropriateness of using organ dysfunction scores as a 'surrogate' for mortality in clinical trials and suggest further work is necessary to better understand the temporal relationship and course of organ failure with mortality.