Diagnostic advantage of droplet digital PCR over blood culture in sepsis: a retrospective study of 115 patients

BACKGROUND: Sepsis is a life-threatening condition that requires rapid and accurate identification of causative pathogens to guide timely antimicrobial therapy. Blood culture is the current diagnostic standard, but it suffers from low sensitivity and long turnaround times. Droplet digital polymerase chain reaction (ddPCR) has emerged as a promising molecular tool that may overcome these limitations. This study aimed to evaluate the diagnostic utility of ddPCR compared with conventional blood culture in patients with sepsis. METHODS: We performed a retrospective study of 115 patients admitted with sepsis to Tianjin First Central Hospital between October 2024 and June 2025. All patients underwent both blood culture and ddPCR testing on admission. Clinical characteristics, laboratory parameters, and infection outcomes were collected. Diagnostic performance, including sensitivity, specificity, positive predictive value, and negative predictive value, was calculated using blood culture as the reference standard. Concordance between ddPCR, blood culture, and non-blood specimen cultures was analyzed. Statistical analysis was performed using descriptive statistics and agreement measures. RESULTS: Blood culture identified pathogens in 27.8% of patients, whereas ddPCR detected organisms in 53%. ddPCR revealed a broader microbial spectrum, particularly Gram-negative bacteria such as Escherichia coli and Klebsiella pneumoniae, and identified mixed infections frequently missed by culture. Within its detection panel, ddPCR demonstrated a sensitivity of 81.3% and specificity of 56.6%, with a high negative predictive value of 88.7%. ddPCR findings showed strong agreement with non-blood culture results in cases where blood cultures were negative, underscoring its clinical relevance. Early in the study, false-positive Candida results were observed but eliminated after stricter aseptic protocols were implemented. CONCLUSIONS: Droplet digital polymerase chain reaction significantly outperformed blood culture in pathogen detection for sepsis, especially for Gram-negative and polymicrobial infections. Its high negative predictive value supports its use as a complementary tool to exclude bloodstream infections and guide early antimicrobial de-escalation. While positive findings must be interpreted with clinical context to avoid overtreatment, ddPCR offers substantial potential to accelerate pathogen identification, improve antimicrobial stewardship, and enhance outcomes in septic patients.