The prognostic importance of interleukin 6 in corona virus disease 2019

Inflammation has a leading role to increase the severity of COVID-19 disease due to induction of a cytokine storm. Inflammatory biomarkers, such as interleukin-6 (IL-6), C-reactive protein (CRP) and procalcitonin (PCT) have been used to predict the progression and mortality of COVID-19. We performed IL-6, CRP and PCT emergency measurements from COVID-19 patients and a prognostic value was evaluated based on these results. We analysed 215 patients retrospectively and devided them into three subgroups according to severity: 1) outpatient subjects with mild symptoms, 2) patients with moderate symptoms (administered to the Infectology) and 3) those with severe symptoms (that required ICU treatment). IL-6 values were measured with chemiluminescence immunoassay (Siemens Advia Centaur XPT) and were compared to CRP and procalcitonin levels. Results were expressed as median (min.-max). The median value of IL-6 was 6.9 ( 55000) pg/mL in severe cases (n=80). All patients with IL-6 level over 15,000 pg/ml died (76% of all deceased patients). We found no correlation between CRP and procalcitonin levels compared to baseline IL-6 levels, however in 90% of severe cases PCT was over 2 μg/L indicating a bacterial or fungal infection which were confirmed with positive haemoculture. In conclusion, according to our results, in COVID-19 patients IL-6 can be used as a prognostic marker, forecasting the development of cytokine storm, which can be also caused by a secondary sepsis supported by high PCT levels and positive haemoculture in our study.