Purpose <p>Mortality and morbidity of patients with bloodstream infection (BSI) remain high despite advances in diagnostic methods and efforts to speed up reporting. This study investigated the impact of reporting rapid Minimum Inhibitory Concentration (MIC)-results in Gram negative BSIs with the ASTar system (Q-linea, Uppsala, Sweden) on the adaptation of empirically started antimicrobial therapy. We performed a real-world study during which antimicrobial susceptibility testing (AST) results were instantly reported to the treating physician in an established multidisciplinary antimicrobial stewardship setting.</p> Methods <p>Consecutive patients with Gram negative bacteremia were included in the study (monomicrobial Gram stain, life expectancy of at least 48&#xa0;h and flagging positive before 2 PM). Rapid AST (RAST) reporting with ASTar was added on top of the standard workflow. Technical performance of the system was evaluated as well as the impact on antimicrobial treatment and timelines of achieving effective and optimal antimicrobial therapy.</p> Results <p>A total of 79 analyses were performed in 77 patients, of which 68 episodes were eligible for analysis. A categorical agreement was observed in 97,5% of 1160 MIC results without false susceptible results. All patients on ineffective empirical therapy (12/68) were switched after a median time of approximately one hour (5&#xa0;min – 15&#xa0;h) after communication of the result. Furthermore, 20/55 non-optimal therapies were adapted within a median period of 3&#xa0;h after communication.</p> Conclusion <p>The implementation of rapid MICs, measured by the ASTar system, in our low antimicrobial resistance setting with elaborate antimicrobial guidelines, was easy and led to early adaptation of empirical treatment in 32/55 instances (12 ineffective and 20 non-optimal therapy).</p> Trial Registration Number <p>NCT06218277 (date of registration: 18–12-2023).</p>