Baseline Procalcitonin Levels and Their Association with Antibiotic Exposure and Clinical Outcomes in Critically Ill Patients with Suspected Bacterial Infection: A Retrospective Cohort Study

Background/Objectives: The excessive use of antibiotics in the intensive care unit (ICU) is driving antimicrobial resistance and poor clinical results. Therefore, the aim of this study was to assess antibiotic exposure and clinical results stratified by baseline procalcitonin (PCT) levels in critically ill ICU patients with suspected bacterial infections. Methods: A retrospective observational cohort study was conducted at a tertiary referral center in Bali, Indonesia. This study included adult ICU patients with suspected bacterial infections and documented baseline PCT levels. Participants were stratified into two cohorts based on a baseline PCT threshold, namely <0.5 ng/mL and ≥0.5 ng/mL. Comprehensive clinical data, antibiotic utilization, and patient results were extracted from electronic medical records. Comparative statistics and multivariable logistic regression were used to identify independent association after adjustment for relevant clinical confounders. Results: In this study, a total of 84 patients were analyzed. Patients in the elevated PCT group (≥0.5 ng/mL) were significantly older and had higher APACHE II scores, suggesting greater baseline illness severity at ICU admission. The median duration of antibiotic therapy was significantly longer in the elevated PCT than the normal group (8 vs. 5 days; p < 0.001). After adjustment for age, APACHE II score, and other relevant clinical variables, elevated baseline PCT levels remained independently associated with prolonged antibiotic exposure and in-hospital mortality. Incremental increases in PCT levels were associated with higher odds of mortality, along with advanced age and higher SOFA scores. Furthermore, the presence of multidrug-resistant (MDR) pathogens was independently associated with prolonged antibiotic use. Conclusions: Elevated baseline PCT levels upon ICU admission were associated with prolonged antibiotic exposure and increased in-hospital mortality. Baseline PCT levels likely reflect underlying illness severity and the magnitude of the host inflammatory response. Within antimicrobial stewardship frameworks, they should be interpreted alongside clinical assessment and severity scores rather than as a standalone determinant of antibiotic duration.