Calibration and discrimination by daily Logistic Organ Dysfunction scoring comparatively with daily Sequential Organ Failure Assessment scoring for predicting hospital mortality in critically ill patients*

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Abstract
The Logistic Organ Dysfunction (LOD) score has been proved effective in evaluating severity during the first day in an intensive care unit but has not been evaluated later. To evaluate attributable mortality related to nosocomial events, organ dysfunction scores that remain accurate throughout the intensive care unit stay are needed. The objective of this study was to evaluate how accurately daily LOD scoring predicts mortality comparatively with daily Sequential Organ Failure Assessment (SOFA) scoring. Prospective multicenter study. Six intensive care units in France. A total of 1685 patients with intensive care unit stays longer than 48 hrs were included in this study (511 hospital deaths). Median age was 66 yrs, and median Simplified Acute Physiology Score II at admission was 38. For each patient, a senior physician recorded the variables needed to compute organ dysfunction scores daily throughout the intensive care unit stay. None. SOFA and LOD scores were computed daily during the first 7 days. Calibration was evaluated based on goodness-of-fit by the Hosmer-Lemeshow chi-square statistic (lower chi-square values and higher p values indicate better fit) and discrimination based on the receiver operating characteristics (ROC) area under the curve (AUC; a ROC-AUC of 1 indicates faultless discrimination and a ROC-AUC of 0.5 indicates the effects of chance alone). Because calibration of both scores was poor at all time points (p < .001), customization was performed using the total score (model 1) or separate introduction of each dysfunction (model 2). The performance of customized LOD and SOFA scores on a given day in predicting mortality was assessed in those patients who spent at least one more calendar day in the intensive care unit. The original LOD and SOFA scores had satisfactory ROC-AUC values (0.720 to 0.766). Internal consistency of both scores was acceptable (p < 10−4 for each organ dysfunction). After customization, the original scores calibrated well between days 1 and 7. Discrimination by both scores was better with model 2 (AUC-ROC, 0.729–0.784). Daily LOD and SOFA scores showed good accuracy and internal consistency, and they could be used to adjust severity for events occurring in the intensive care unit.