Diagnostic and prognostic performance of procalcitonin among hospitalized adults with suspected bacterial infection in Southwest Ethiopia: a prospective observational study

Bacterial infections are widespread in developing countries including Ethiopia, contributing to rising morbidity and mortality rates. Procalcitonin (PCT) is widely used to assess the severity of bacterial infections and to guide antibiotic treatment decisions. Despite its significance, there is lack of comprehensive data regarding the performance of PCT in the diagnosis and treatment monitoring of bacterial infections. The primary objective was to evaluate the diagnostic performance of admission PCT for identifying bacterial infection. The secondary objectives were to assess its prognostic performance for identifying qSOFA-based sepsis and its association with clinician-directed antibiotic discontinuation. A hospital-based longitudinal study design was employed among admitted patients at Jimma Medical Center (JMC) from May to November 2025. The study participants were selected consecutively until the expected sample size was achieved. Structured questionnaire was used to collect sociodemographic data, clinical information, and laboratory data. PCT was assessed at admission and on day 3 of hospitalization. The data was analyzed using Statistical Package for Social Science (SPSS) software version 27. Receiver Operating Characteristic (ROC) curve was used to assess the sensitivity, specificity, and overall diagnostic performance of PCT for bacterial infections. Multivariate regression models were employed to control potential confounding variables. P-value < 0.05 with 95% CIs were considered statistically significant. A total of 210 hospitalized adults with suspected bacterial infection were included in the study. The mean admission PCT was 1.65 ± 2.1 ng/mL. Admission PCT demonstrated poor diagnostic discrimination for identifying bacterial infection, with an AUC of 0.56 (95% CI: 0.45–0.68), corresponding to a sensitivity of 57% and specificity of 60% at an optimal cutoff of 0.465 ng/mL. In contrast, PCT showed good discrimination for identifying participants meeting the study-defined qSOFA-based sepsis classification, with an AUC of 0.83 (95% CI: 0.738–0.928). The optimal cutoff for sepsis was 2.65 ng/mL, yielding a sensitivity of 82% and specificity of 85%. Among the 50 participants who underwent repeat PCT measurement on day 3, serial PCT decline was significantly associated with clinician-directed antibiotic discontinuation. Day-3 PCT demonstrated excellent discriminatory performance for this outcome, with an AUC of 0.926 (95% CI: 0.836–1.00) and both sensitivity and specificity of 90%. The overall in-hospital mortality rate was 6.7% (14/210), and in an exploratory multivariable analysis, qSOFA-based sepsis classification was associated with higher odds of mortality, although the estimate was imprecise because of the small number of deaths. Among hospitalized adults with suspected bacterial infection, admission PCT was not reliable for identifying bacterial infection but showed good performance for qSOFA-based sepsis identification and was strongly associated with clinician-directed antibiotic discontinuation. The latter finding should be interpreted cautiously because serial PCT analysis was exploratory and limited to a selected subgroup. Not applicable.