ObjectiveThe study investigates the diagnostic and prognostic value of C-reactive protein (CRP) and procalcitonin (PCT) in patients with sepsis and septic shock.BackgroundLimited data regarding the prognostic value of CRP and PCT during the course of sepsis or septic shock is available.MethodsConsecutive patients with sepsis and septic shock from 2019 to 2021 were included monocentrically. Blood samples were retrieved from the day of disease onset (day 1), day 2, 3, 5, 7, and 10. Firstly, the diagnostic value of CRP and PCT for the diagnosis of a septic shock, as well as for the discrimination of positive blood cultures, was tested. Secondly, the prognostic value of the CRP and PCT was tested for 30-day all-cause mortality. Statistical analyses included univariablet-tests, Spearman’s correlations, C-statistics, and Kaplan–Meier analyses.ResultsA total of 349 patients were included, of which 56% had a sepsis and 44% a septic shock on day 1. The overall rate of all-cause mortality at 30 days was 52%. With an area under the curve (AUC) of 0.861 on day 7 and 0.833 on day 10, the PCT revealed a superior AUC than the CRP (AUC 0.440–0.652) with regard to the discrimination between patients with sepsis and septic shock. In contrast, the prognostic AUCs for 30-day all-cause mortality were poor. Both higher CRP (HR = 0.999; 95% CI 0.998–1.001;p= 0.203) and PCT levels (HR = 0.998; 95% CI 0.993–1.003;p= 0.500) were not associated with the risk of 30-day all-cause mortality. During the first 10 days of ICU treatment, both CRP and PCT declined irrespective of clinical improvement or impairment.ConclusionPCT was a reliable diagnostic tool for the diagnosis of septic shock compared to CRP. Both CRP and PCT were shown to have poor predictive value with regard to 30-day all-cause mortality and were not associated with the risk of all-cause mortality in patients admitted with sepsis or septic shock.