Backgroundaccompanied to the spreading of coronavirus disease 2019 (Covid-19) in the world, identifying factors related to the severity of the disease is one of the interests of physician and medical researchers. We hypothesized that interleukin 6 serum level is associated with severe outcome.MethodsIn this longitudinal prospective cohort study we enrolled 208 confirmed COVID-19 patients who were admitted to the Tohid Hospital (Sanandaj, Iran). Patients were classified into two groups based on IL-6 value in the first day of admission, elevated (n = 107) or not elevated/normal (n = 101), and followed until the occurrence of final outcome (death or discharge from the hospital). Data were analyzed using univariate methods, Chi-squared and independent two sample T test. The relationship between the independent variables and our interesting outcomes were investigated by multiple linear and penalized logistic regression modeling.ResultsA total of 208 patients, 51% female and mean age 53.6 ± 16.3 years, including 107 elevated and 101 non-elevated IL-6 patients, were followed. No significant difference was observed between the two groups in demographic and clinical characteristics. Although not significant, logistic regression results showed that the chance of death occurrence among patients with elevated IL-6 are 3.91 times higher. According to the multiple linear regression modeling, elevated IL-6 significantly increased the duration of hospital stay (P = 0.02). Frequency of ICU admission (P = 0.04) and mean of ICU stay (P = 0.8) are also higher in elevated IL-6 group.ConclusionThis study revealed that elevated IL-6 is significantly related to prolongation of hospital stay in Covid-19 patients. Although not significant, the occurrence of death among patients who had increased IL-6 in the time of admission was higher than patients with normal or lower serum levels of IL-6.