Purpose. To investigate whether absolute value of procalcitonin (PCT) or the change (delta-PCT) is better indicator of infection in intensive care patients. Materials and Methods. Post hoc analysis of a prospective observational study. Patients with suspected new-onset infection were included in whom PCT, C-reactive protein (CRP), temperature, and leukocyte (WBC) values were measured on inclusion (t0) and data were also available from the previous day (t-1). Based on clinical and microbiological data, patients were grouped post hoc into infection- (I-) and noninfection- (NI-) groups. Results. Of the 114 patients, 85 (75%) had proven infection. PCT levels were similar at t-1: I-group (median [interquartile range]): 1.04 [0.40–3.57] versus NI-group: 0.53 [0.16–1.68], p=0.444. By t0 PCT levels were significantly higher in the I-group: 4.62 [1.91–12.62] versus 1.12 [0.30–1.66], p=0.018. The area under the curve to predict infection for absolute values of PCT was 0.64 [95% CI = 0.52–0.76], p=0.022; for percentage change: 0.77 [0.66–0.87], p<0.001; and for delta-PCT: 0.85 [0.78–0.92], p<0.001. The optimal cut-off value for delta-PCT to indicate infection was 0.76 ng/mL (sensitivity 80 [70–88]%, specificity 86 [68-96]%). Neither absolute values nor changes in CRP, temperature, or WBC could predict infection. Conclusions. Our results suggest that delta-PCT values are superior to absolute values in indicating infection in intensive care patients. This trial is registered with ClinicalTrials.gov identifier: NCT02311816.