Early diagnostic value of serum procalcitonin, C-reactive protein, white blood cell count and the neutrophil percentage in bacterial and fungal bloodstream infections

Bloodstream infections (BSIs) are severe systemic disorders caused by pathogenic microorganisms, including bacteria and fungi, invading the bloodstream. Associated with high morbidity and mortality, BSIs represent one of the leading causes of death globally. There is an urgent demand for simple, rapid, and accurate laboratory biomarkers to facilitate the diagnosis and differential diagnosis of patients with suspected BSIs, thereby guiding timely and targeted antimicrobial therapy. To evaluate the value of serum procalcitonin (PCT), C-reactive protein (CRP), white blood cell count (WBC), and neutrophil percentage (NEUT%) for early and differential diagnosis of bacterial vs. fungal bloodstream infections (BSIs), a cross-sectional study was conducted. A total of 1649 patients with suspected BSI were included in this retrospective study. Of these, 1357 patients with positive blood cultures were classified as the BSI group (experimental group), and 292 patients with negative blood cultures were assigned to the non-BSI group (control group). Serum PCT, CRP, WBC/NEUT% were measured using a bioMerieux VIDAS 30 analyzer, SIEMENS ADVIA 2400 and by Sysmex XN-9000, respectively. Microbial identification was based on bioMerieux VITEK 2 systems. The diagnostic performance of these biomarkers in the discrimination in bacterial and fungal bloodstream infections were compared using receiver operating characteristic (ROC) curves. For BSI discrimination, a PCT level > 0.687 ng/mL could demonstrate the optimal performance (AUC = 0.788, sensitivity 61.7%, specificity 80.1%). The PCT level < 0.5 ng/mL for 3 consecutive days could effectively rule out BSI (sensitivity 98.1%, specificity 79.5%). Elevated PCT (> 1.78 ng/mL) and CRP (> 79.76 mg/L) levels were associated with bacterial BSIs (AUC = 0.686 for the combined markers). A PCT level > 1.98 ng/mL suggested Gram-negative BSI (sensitivity 68.4%). The positive diagnostic rates of the PCT + CRP+NEUT% combined test for G- bacterial and G+ bacterial BSIs reached 96.17% and 92.86% respectively, which significantly improved the diagnostic positive rate compared with single diagnosis. PCT could reliably excludes BSI (3-day < 0.5 ng/mL rule) and aids differentiation (bacterial/fungal: PCT + CRP; G-/G+: PCT+NEUT%). Multi-parameter approaches optimize diagnostic accuracy for timely intervention.