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

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.