Diagnostic utility of procalcitonin in determining Gram-negative and Gram-positive bacterial bloodstream infections: a single-centre study from South India

Background Bloodstream infections (BSIs) are significant contributors to global morbidity and mortality, with sepsis accounting for 11 million deaths annually. Accurate and rapid diagnosis is essential for effective management. Methods This retrospective analysis was conducted on 275 positively flagged blood culture bottles collected over one year. Samples were processed using automated blood culture systems, followed by pathogen identification and antimicrobial susceptibility testing (AST) via the Vitek-2 Compact system (bioMérieux, France). PCT (Procalcitonin) levels were measured using MINIVIDAS (bioMérieux, France) and correlated with pathogens to evaluate diagnostic accuracy. Results Among 251 isolates, Gram-negative bacteria predominated (77.68%), with Enterobacterials like Escherichia coli (46.3%) and Klebsiella pneumoniae (44.29%) being the most common. GP (Gram-positive) bacteria accounted for 22.31%, led by Staphylococcus aureus and Enterococcus species. The mean PCT levels were higher in GN (Gram-negative) infections (37.87 ng/mL) than in GP infections (35.09 ng/mL). PCT demonstrated a sensitivity of 77.41%, specificity of 91.04%, and diagnostic accuracy of 82.87%. Conclusion PCT levels were elevated in both Gram-negative and Gram-positive BSIs, with marginally higher values in Gram-negative infections. Significant elevations in Gram-positive infections, particularly with Streptococcus and Staphylococcus species, highlight their broader diagnostic relevance. With good sensitivity and high specificity, PCT serves as a useful adjunctive biomarker for early BSI detection and may support preliminary differentiation of pathogen groups when interpreted alongside clinical and microbiological findings.