How do IL-6 levels correlate with disease severity in COVID-19 patients? A Retrospective Cohort Study

Aims: The ongoing COVID-19 pandemic has presented unprecedented challenges to healthcare systems globally, with over 4,000 new COVID-19 patients admitted into hospital daily in the UK in January 2021 (Karjalainen, 2021). This study investigates the relationship between IL-6 levels in inpatient COVID-19 patients and the severity of infection. Methods: We conducted a retrospective analysis of 227 COVID-19 patients admitted to King’s College Hospital, London. Patient data encompassed C-reactive protein (CRP), interleukin-6 (IL-6), interleukin-8 (IL-8), and tumour necrosis factor (TNF) levels. Mean IL-6 values and standard deviations were computed for patients undergoing each respiratory support method (intubation, CPAP, Optiflow), for those who survived and those who succumbed to COVID-19, and in relation to their reported MRC dyspnoea score (0-4). Results: Mean IL-6 levels were 2.1 times higher in deceased patients than those discharged alive (233 vs 110). Mean IL6 levels were highest in patients who were intubated (143), followed by patients on CPAP (115), with lowest levels in patients on Optiflow (103). There was a weak correlation between IL-6 levels and MRC dyspnoea score. IL-6 levels varied more than other inflammatory markers in response to severity of infection. Conclusions: Our findings indicate a positive correlation between the levels of IL-6 in patients and the severity of infection. This lends support to the consideration of IL-6 as a valuable factor in both risk stratification and the monitoring of disease progression in individuals with COVID-19.