Monocyte distribution width as an adjunctive biomarker for differentiating pulmonary tuberculosis from cavitary nontuberculous mycobacterial pulmonary disease

Rapid discrimination between pulmonary tuberculosis (PTB) and nontuberculous mycobacterial pulmonary disease (NTM-PD) remains clinically challenging, particularly in cavitary disease where radiological findings may overlap. Monocyte distribution width (MDW), automatically reported by contemporary hematology analyzers, has emerged as a potential biomarker of systemic immune activation; however, its role in differentiating PTB from cavitary NTM-PD remains unclear. We retrospectively reviewed the records of consecutive patients diagnosed with PTB or NTM-PD at our institution between May 2021 and February 2025. All PTB cases were confirmed by culture and/or nucleic acid amplification testing (NAAT) identifying Mycobacterium tuberculosis; no cases were diagnosed solely on smear positivity. Clinical characteristics and laboratory data, including MDW, were compared between groups. Multivariable logistic regression analyses were performed using prespecified parsimonious models to minimize overfitting. Of the 115 patients, 73 had PTB and 42 had NTM-PD, including 18 with cavitary NTM-PD. Compared with patients with cavitary NTM-PD, patients with PTB had significantly lower lymphocyte counts and hemoglobin and albumin levels, and higher C-reactive protein levels and MDW. In multivariable analysis comparing all PTB cases with cavitary NTM-PD, MDW demonstrated a directional association with PTB after adjustment for radiological extent (adjusted OR 1.37, 95% CI 0.98–1.92, P = 0.066), whereas radiological grade remained independently associated (adjusted OR 0.15, 95% CI 0.04–0.52, P = 0.003). Receiver operating characteristic analysis of MDW yielded an area under the curve of 0.779, which should be interpreted as exploratory given the limited sample size and lack of independent significance. In this single-center retrospective study, MDW demonstrated a directional association with PTB and may provide adjunctive information during early clinical assessment of cavitary mycobacterial disease while awaiting microbiological confirmation. However, MDW was not independently predictive after multivariable adjustment, and its discriminatory performance should be interpreted cautiously. Larger prospective, multicenter studies are required to validate these findings.