Rapid Diagnostics and Rapid Antimicrobial Susceptibility Testing for Bloodstream Infections: A Narrative Review and...

Bloodstream infection is a time-critical syndrome in which antimicrobial treatment is usually started before definitive microbiological information is available. Conventional blood culture remains essential because it recovers viable organisms and enables phenotypic antimicrobial susceptibility testing, but its sequential workflow often cannot inform the earliest treatment decisions. This narrative review examines rapid organism identification, molecular and nonmolecular resistance-marker methods, and rapid phenotypic susceptibility testing, and proposes a clinical actionability framework for implementation. PubMed, Embase, Web of Science, and the Cochrane Library were searched for publications from January 2010 through April 2026, with priority given to guidelines, systematic reviews, randomized trials, multicenter studies, and implementation research. Across technologies, the most reproducible benefits are shorter time to active or optimal therapy, earlier escalation when empirical treatment is inactive, and earlier de-escalation when narrower therapy is safe. Effects on mortality, length of stay, and cost are less consistent. The 2015 multiplex polymerase chain reaction trial and the RAPIDS-GN trial showed faster antimicrobial modification. In the 2026 FAST trial, rapid phenotypic susceptibility testing did not demonstrate superiority for a 30-day desirability-of-outcome ranking endpoint, although escalation or de-escalation occurred earlier. These findings support a conditional rather than technology-centered interpretation of benefit. Actionability depends on five interacting domains: the type and certainty of the result, patient risk, the pretest probability of resistance, the institution's result-to-action capacity, and the quality of antimicrobial stewardship interpretation. Molecular panels and resistance markers are most useful when identity or a positive marker has an immediate therapeutic or infection-control consequence; rapid phenotypic testing is most useful when drug-specific susceptibility is the remaining decision bottleneck. The proposed framework is a heuristic derived from narrative evidence synthesis and author judgment, not a validated clinical score. Prospective validation and local adaptation are required.