Comparative Receiver operating characteristic curves for early sepsis diagnosis. The curves relate the different models of logistic regression detailed in Table 4: M1: sepsis score >7; ACTH ≤ 233 nM/L; cortisol ≥ 450 nM/L, M2: PCT >2 ng/mL; ACTH ≤ 233 nM/L; cortisol ≥ 450 nM/L, M3: ACTH ≤ 233 nM/L; cortisol ≥ 450 nM/L, M4: PCT >2 ng/mL, M5: sepsis score >7. Sepsis score is a recommended clinico-biological multiple variable score [17, 18], ACTH and cortisol baseline are a combination of two HPA biological stress parameters, and blood PCT is a gold standard biological marker of sepsis [13, 50]. Respective AUC values are expressed in Table 4. The three combination panels including the two selected gold standards: sepsis score or PCT (in M1 and M2), performed for the best and similarly and offered added-value to each selected gold standard individually (that is, sepsis score (in M5) or PCT (in M4)): P = 0.005 and P < 0.001, respectively. On the other hand, adding sepsis score or PCT to the two combinations of stress parameters (ACTH, cortisol baseline) also optimized the prediction vs. ACTH and cortisol baseline: P = 0.037 and P = 0.036, respectively. Vertical axis represents the number of true positive values (sensitivity) and horizontal axis the number of false positive values (1-specificity), with the diagonal segments produced by ties.