From sepsis to COVID-19: the emerging role of Monocyte Distribution Width (MDW)

Immune activation of the monocyte-macrophage population plays a pivotal role in the systemic hyper-inflammatory response, typically observed during severe dysimmune diseases, such as sepsis and COVID-19. In this commentary, we have reviewed the literature data on the novel cytometric marker of monocyte activation, known as MDW (Monocyte Volume Distribution Width), a monocyte dimensional parameter obtainable by blood count examination, which has recently been approved for clinical use as "Early Sepsis Indicator" (ESId), in patients accessing the Emergency Department. In particular, in this Opinion paper, we highlight the main clinical applications and relevant perspectives of this new test: from its use for (early) diagnosis of sepsis, in different hospital settings, to its emerging prognostic role in patients with COVID-19, as a biomarker of disease severity. In view of the reported evidence, we discuss the clinico-pathological notion that, basically, severe COVID-19 can be considered a new form of viral sepsis. Further clinical studies are needed to better understand the pre-analytical and analytical variables of this parameter, correlate MDW dynamics with those of other humoral and cytometric markers, and validate the new diagnostic and prognostic applications of MDW on large multicenter case series.