The AUC for S100A9 combined with lactate and APACHE II in estimating the risk of septic shock improved from 0.74 (95% CI 0.68–0.79, P < 0.001) to 0.81 (95% CI 0.76–0.86, p < 0.001), and the sensitivity for detecting septic shock was also improved (from 65.50% to 74.20%)(Fig 2B, Table 4). Here, S100A9 is linked to septic shock.