After surgery, PCT levels were significantly higher in the delirium group than in patients without delirium on admission to the ICU (day 0: 0.08 ng/mL, IQR 0.03–0.15 vs. 0.05 ng/mL, IQR 0.02–0.09, p = 0.011) and for the consecutive days (day 1: 0.59 ng/mL, IQR 0.25–1.55 vs. 0.25 ng/mL, IQR 0.14–0.54, p = 0.003; day 2: 1.21 ng/mL, IQR 0.24–3.29 vs. 0.36 ng/mL, IQR 0.16–0.76, p = 0.006; day 3: 0.76 ng/mL, IQR 0.48–2.34 vs. 0.34 ng/mL, IQR 0.14–0.66, p = 0.001, respectively, in the delirium and non-delirium group), with a peak value on the second day after surgery (Figure 3). The gene discussed is CALCA; the disease is delirium.