Inflammatory markers best discriminate between patients with uncomplicated HMs and patients with HLH in the context of HMs. (A) CART, including initial assessment of all markers, is shown. CART analysis determines the relative importance of different variables for identifying homogeneous groups within a data set. CART’s growth limits were defined with the Gini method, limiting 4 cases in the child node and 5 cases in the parent node. The minimum change in improvement was defined as 0.0001 and pruning with the minimum difference in risk of 1 standard error. (B) ROC analysis for individual HLH-defining markers at presentation (initial measurement) is shown. The distribution of maximally pathologic values during the index encounter is shown in supplemental Figure 4. The dotted line indicates the pertinent point on the curve identified as the best balance between sensitivity and specificity (with the highest Youden index). (C) The table summarizes the performance of each marker and thresholds defined by the HLH-2004 and ROC analyses. AUC, 95% CIs, P values, sensitivity (Sens), and specificity (Spec) for the HLH-2004 thresholds and the optimized ones at initial presentation are presented. ANC, absolute neutrophil count; Tg, triglycerides.