BACKGROUND: Fast diagnostic tests providing earlier identification (ID) of pathogens, and antimicrobial susceptibility testing (AST) may reduce time to appropriate antimicrobial therapy (AAT), decrease mortality, and facilitate antimicrobial deescalation (ADE). Our objective was to determine the theoretical reduction in time to AAT and opportunities for ADE with Accelerate PhenoTM System (AXDX). METHODS: The prospective cohort (April 14, 2016 through June 1, 2017) was from the Barnes-Jewish Hospital, a 1250-bed academic center. Emergency department (ED) or intensive care unit (ICU) blood cultures Gram-stain positive for gram-negative bacilli (GNB) or yeast. AXDX was used in parallel with standard-of-care (SOC) diagnostics to determine differences in time to pathogen ID and AST. Theoretical opportunities for ADE from AXDX results were determined. RESULTS: In total, 429 blood cultures were screened, 153 meeting inclusion criteria: 110 on-panel GNB, 10 Candida glabrata, and 5 Candida albicans. For GNB SOC, median time from blood culture positivity to ID and AST were 28.2 and 52.1 h. Median time to ID and AST after AXDX initiation was 1.37 and 6.7 h for on-panel organisms. For on-panel Candida, time to ID was approximately 21 h faster with AXDX. ADE or AAT was theoretically possible with AXDX in 48.4%. Of on-panel organisms, 24.0% did not receive initial AAT. In-hospital mortality was 46.7% without initial AAT, and 11.6% with AAT. Coverage of AXDX was 75.3%, specificity 99.7%, positive predictive value (PPV) 96.0%, and negative predictive value (NPV) 97.6%. On-panel sensitivity was 91.5%, specificity 99.6%, PPV 96.0%, and NPV 99.0%. CONCLUSIONS: AXDX provides more rapid ID and AST for GNB and ID for yeast than SOC. AXDX could potentially reduce time to AAT and facilitate ADE.