High serum IL-6 values increase the risk of mortality and the severity of pneumonia in patients diagnosed with COVID-19

•The serum IL-6 level is the best marker for the severity of COVID-19 of those tested.•IL-6 values greater than 35 pg/mL can differentiate between mild and severe COVID-19.•High serum IL-6 values are associated with increased risk of mortality and ICU admission. The clinical presentation of COVID-19 is very heterogeneous, ranging from asymptomatic to severe, which could lead to the need for mechanical ventilation or even death.We analyzed the serum levels of IL-6 in patients with COVID-19 diagnosis and its relationship with the severity of the disease, the need for mechanical ventilation and with patient mortality. We assessed IL-6 in a cohort of 50 patients diagnosed with COVID-19 pneumonia with different degrees of disease severity, and compared it with clinical and laboratory findings. We found higher levels of IL-6 in patients with more severe pneumonia according to CURB-65 scale (p = 0.001), with ICU mechanical ventilation requirements (p = 0.02), and who subsequently died (p = 0.003). Of the clinical and analytical parameters analyzed in the current study, the serum levels of IL-6 was the most effective predictor of disease severity. From the data obtained in ROC curve analysis, we defined a cut-off point for serum IL-6 levels of 35 pg/mL above which both the risk of mortality (OR = 20.00, 95 % CI 4.214-94-912, p = 0.0001) and ICU admission (OR = 12.750, 95 % CI 2,159-75,3,3, p = 0.005) were increased. Starting from blood IL-6 levels 27 out of 50 patients, with high levels and more severe symptoms, were treated with the IL-6 receptor antagonist Tocilizumab. IL-6 serum levels appear to be a useful prognostic biomarker in patients with a diagnosis of COVID-19 pneumonia. A cut-off point of 35 pg/mL could clearly differentiate patients a with more severe disease.