Figure 2.

Receiver operating characteristics of late anemia prediction model and correspondence with point system. (a) The receiver operating characteristic (ROC) of the model predicting late anemia. Higher sensitivity (S) is associated with a lower threshold for positivity (T', probability of meeting criteria for late anemia). Accordingly, a higher proportion of the population will be declared to meet late anemia criteria (P') as specificity decreases. For example, a desired sensitivity of 60% would entail declaring a threshold for positivity corresponding to a probability of late anemia of 22% or more (T'). This results in 34% of the population exceeding this predicted probability and thus at risk for late anemia (P'). (b) Correspondence between intensive care unit (ICU) anemia points (see the text) and the ROC curve. Determining a lower point threshold of unacceptable risk of late anemia entails a trade-off between higher sensitivity and the willingness to declare a higher proportion of the population at risk. Setting a threshold of 21 points, which would achieve a sensitivity of 60% in identifying patients meeting criteria for late anemia, would result in considering intervention in 34% of the population (a). On the assumption that the proposed intervention is recombinant human erythropoietin, considering all ICU patients for treatment would result in 100% sensitivity, but no specificity (point A). Using inclusion criteria for the Corwin study results in 77% sensitivity and 65% specificity as illustrated by point B (see the text and Table 4), which is comparable to the point-based system. The ICU anemia score permits earlier intervention with comparable predictive power.