Rapid commercial CTX-M diagnostics: Performance, limitations and clinical impact

CTX-M enzymes account for more than 90% of all extended-spectrum β-lactamases (ESBLs) identified in Enterobacterales. Therefore, rapid identification of these enzymes could improve clinical outcomes in patients infected or colonized by such pathogens. In this review, we described the characteristics and limitations of commercially available rapid tests for detecting CTX-M proteins (lateral flow immunoassays) or bla_CTX-M genes (microarrays, quantitative PCR, or loop-mediated isothermal amplification). Additionally, we summarized and discussed their potential clinical impact. Some commercial CTX-M assays - particularly those analyzing aliquots from positive blood cultures (i.e., Verigene, BioFire FilmArray, ePlex) - demonstrated clear advantages over standard-of-care methods, shortening the interval to effective therapy and improving overall patient outcomes. However, the widespread adoption of these rapid assays in routine laboratories remains limited due to several factors, including high costs and the lack of robust evidence supporting their positive impact. To address these implementation challenges, laboratories should focus on a defined patient subgroup in whom the application of these assays is likely to yield the greatest clinical impact. In particular, we propose that all laboratories at least perform rapid CTX-M assays on all Gram-negative-positive blood cultures (including those with sterile fluids) obtained from critically ill patients, such as ICU-patients with septic shock. This strategy is best when accompanied by active communication between the laboratory and key stakeholders in patient management. Providing rapid results for this subpopulation of patients may facilitate timely initiation of appropriate therapy and ultimately improve patient outcomes.