Early increased monocyte-to-lymphocyte ratio as a potential biomarker of bacterial sepsis in patients with severe COVID-19.

Monocytes are pivotal during inflammation. Sepsis added to COVID-19 increases mortality and inflammation. However, the role of monocytes in this condition is unclear. Our aim was to determine monocyte frequencies and HLA-DR expression related to size distribution in patients with severe COVID-19 with or without sepsis. Twenty-nine patients with COVID-19, 9 patients with COVID-19 + sepsis, and 11 non-COVID nonseptic volunteers were recruited. Patients with COVID-19 + sepsis had increased monocyte count (P = 0.004) and monocyte-to-lymphocyte ratio (MLR, P = 0.01) prior to bacterial sepsis development. The monocyte-to-lymphocyte ratio had an area under the curve of 77.8%, suggesting its potential utility in predicting bacterial sepsis up to 21 d before positive culture. In these patients, smaller intermediate and nonclassical monocytes expressed higher levels of HLA-DR (P < 0.05). Diminished HLA-DR expression in bigger monocytes was associated with an increase in severity and inflammatory markers (r2 values equal to or higher than ±0.4, P < 0.05). Our results suggest that the monocyte-to-lymphocyte ratio could be a potential early marker for bacterial sepsis development in patients with severe COVID-19.