Abstract
BACKGROUND: MRSA bacteremia requires early anti-MRSA therapy, as beta-lactams are ineffective; delays for pathogen identification and susceptibility results can worsen outcomes. Rapid biomarkers are thus essential. Cell population data (CPD), captured via flow cytometry by automated hematology analyzers, appears earlier than conventional laboratory changes but is not reported to clinicians. CPD is readily available at no extra cost and shows promise for early exacerbation detection, though its utility remains underexplored. [Figure: see text] [Figure: see text] METHODS: We retrospectively analyzed MRSA bacteremia cases at Saitama Medical Center, a tertiary hospital in Japan (April 2018–March 2021). Patients were grouped into appropriate therapy (AT; anti-MRSA agents) or inappropriate therapy (IT; non-anti-MRSA agents) (Fig. 1). Hematologic parameters, including CPD from XN-9000 analyzers (Sysmex Corp., Japan), were collected before and after antibiotic initiation; post-/pre-treatment ratios were calculated to minimize interpatient variability. Univariate analyses assessed patient characteristics and laboratory value ratios between groups. Logistic regression adjusting for significant covariates evaluated therapy appropriateness. A multivariable model yielded a composite score, and its diagnostic performance was evaluated. [Figure: see text] [Figure: see text] RESULTS: Fifty-two patients (AT 32, IT 20) were analyzed. Univariate analysis identified four significant factors: blood sampling interval and changes in lymphocyte (%), NE-SFL, and NE-FSC (both CPD parameters) (Table 1, 2). No strong multicollinearity was observed among these three markers (r = −0.11 to +0.35). A composite model from multivariable logistic regression adjusted for the interval and including lymphocyte (%), NE-SFL, and NE-FSC showed excellent discrimination (AUC 0.93, 95 % CI: 0.86–1.0), with sensitivity 0.90, specificity 0.88, PPV 0.82, and NPV 0.93 (Fig. 2). CONCLUSION: Neutrophil-related CPD parameters quickly reflected treatment appropriateness in MRSA bacteremia. A composite score derived from lymphocyte (%), NE-SFL (nucleic acid content), and NE-FSC (cell size) may enable early recognition of ineffective therapy. As CPD is routinely collected without added cost or procedures, it offers a practical biomarker to prompt timely anti-MRSA adjustments. DISCLOSURES: All Authors: No reported disclosures