Diagnostic performance and cost-effectiveness of a combined rapid antimicrobial susceptibility testing (RAST) and...

To evaluate the diagnostic performance, clinical impact, and cost-effectiveness of a workflow combining EUCAST rapid antimicrobial susceptibility testing (RAST) with lateral flow immunochromatographic assays (LFIA) for resistance detection directly from positive blood cultures (BCs).

A single-center, retrospective study including 179 monomicrobial bloodstream infection (BSI) episodes was conducted. RAST results were compared with broth microdilution (BMD) as the reference method. LFIA performance was assessed for the detection of extended-spectrum β-lactamases (ESBLs) and carbapenemases. The impact on antimicrobial therapy was analyzed at predefined time points. A cost-effectiveness analysis using a decision tree model compared three strategies: matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) identification plus RAST, MALDI-TOF MS plus LFIA and RAST, and the FilmArray BCID2 molecular panel.

Overall categorical agreement between RAST and definitive AST was 98.2%, with a low rate of very major errors (n = 8). LFIA showed excellent performance, with 100% concordance for ESBL and carbapenemase detection. Antimicrobial therapy was modified in 54.2% of patients, with most changes occurring after direct identification and LFIA results. In 97% of cases with therapeutic modification, treatment was appropriate according to definitive AST. In the economic analysis, MALDI-TOF MS plus LFIA and RAST showed a favorable balance between cost (€34.32 per patient) and effectiveness (16.51 h gained), compared with MALDI-TOF MS plus RAST alone (€10.94; 15.11 h) and BCID2 (€160.60; 20.43 h). The incremental cost-effectiveness ratio for adding LFIA was €16.59 per hour gained.

The combination of RAST and LFIA directly from positive BCs provides rapid, accurate, and cost-effective microbiological information, supporting early optimization of antimicrobial therapy and representing a practical alternative to molecular syndromic panels for BSIs.