Sepsis is a global health problem, annually over 45 million patients are diagnosed and over 11 million deaths are recorded. Activation of monocytes in sepsis by the pathogen agent or hypoxia brings about functional, morphological and phenotypic changes in these cells. Monocyte Distribution Width (MDW) is a new biomarker, defined as a measure of monocyte size heterogeneity and has been approved by the Food and Drug Administration for the early diagnosis of sepsis in the adult patient in the emergency department. In intensive care services, this biomarker can be used as a prognostic index in the follow-up of patients with sepsis. The indicator is a measure of the increased morphological variability of monocytes in response to infections, regardless of bacterial, viral or fungal etiology. This new marker also has increased values in the infection with COVID-19 and correlates positively with the severity of the disease.