Direct rapid antimicrobial susceptibility testing (RAST) from positive blood cultures: Recent advances, challenges, and future directions

Bloodstream infections (BSIs) carry high morbidity and mortality, and delayed targeted therapy worsens survival. Conventional antimicrobial susceptibility testing (AST) from positive blood cultures typically requires 24–48 h (and >72 h for some resistant organisms), delaying appropriate treatment and leaving 14–78% of empirical regimens unnecessary or ineffective. Direct rapid antimicrobial susceptibility testing (RAST) addresses this bottleneck by delivering AST in 4–16 h with categorical agreement (CA) ≥90% for major pathogens, using volatile organic compound (VOC) detection, modified disk diffusion, microfluidics, and molecular approaches. RAST generally makes susceptibility results available approximately 8–44 h earlier, with savings exceeding 56 h when conventional testing requires more than 72 h. This review compares the principles, turnaround times (TAT), and performance of leading RAST platforms. It further identifies persistent bottlenecks restricting cross-platform comparability and clinical uptake, most notably the absence of standardized protocols, the inability of molecular assays to determine minimum inhibitory concentrations (MICs), and unresolved pre-analytical confounders. Although RAST reliably shortens time-to-result and supports antimicrobial stewardship, its routine integration demands platform-specific validation, transparent regulatory and cost-effectiveness assessment.