Utility of monocyte distribution width as a rapid biomarker for severity assessment in bacterial pneumonia: a retrospective study

Background Monocyte distribution width (MDW) has been proposed as an indicator of sepsis. Because MDW can be measured within approximately 1 min as part of routine white blood cell differential analysis, it may serve as a practical tool for rapid assessment of bacterial pneumonia severity. However, established biomarkers such as procalcitonin (PCT) require additional processing time and cost. Methods This retrospective study included 252 patients hospitalised with bacterial pneumonia. Disease severity was assessed using the sequential organ failure assessment (SOFA), age, dehydration, respiration, orientation, and pressure (A-DROP), and pneumonia severity index (PSI) scoring systems. The predictive performance of WBC count, C-reactive protein levels, MDW, and PCT levels was analysed. Correlation analysis between MDW and PCT levels was also performed. Results Both MDW and PCT were independently associated with A-DROP and SOFA scores in multivariable analyses, whereas only PCT was associated with PSI score. A moderate positive correlation was observed between MDW and PCT levels (r = 0.6763, p < 0.001). ROC analysis showed that PCT had the highest discriminatory performance (AUC 0.664), whereas MDW demonstrated modest but clinically informative performance (AUC 0.597). Conclusions PCT remains a robust indicator of bacterial pneumonia severity. MDW may serve as a rapid, cost-effective adjunct biomarker that supports early clinical assessment, particularly in time-sensitive settings such as the emergency department, where immediate decision-making is required.