Abstract
Background: Interleukin-6 (IL-6) is a pro-inflammatory cytokine that is produced at varying levels in patients with coronavirus disease 2019 (COVID-19). The neutrophil-lymphocyte ratio (NLR) is one of the new inflammatory markers of COVID-19. This study aimed to evaluate the differences in IL-6 level and the NLR in mild and severe COVID-19 and assess their correlation with COVID-19 severity and the correlation of IL-6 and NLR in COVID-19. Methods: A total of 91 patients with COVID-19 were divided into mild (n = 57) and severe (n = 34) COVID-19 groups. IL-6 levels were measured using the electrochemiluminescence immunoassay method on Roche Cobas e411. The NLR was the ratio of the total neutrophil and lymphocyte counts from complete haematology on the Sysmex XS-800i. Data were analysed using the Kolmogorov-Smirnov, Mann-Whitney, receiver operating characteristic curve, chi-square and Spearman correlation tests. The statistical test was significant at p <0.05. Results: Serum IL-6 levels and NLR significantly differed in mild and severe COVID-19. The median (min-max) IL-6 levels for mild and severe COVID-19 were 3.59 (1.50-638.30) pg/mL and 28.82 (5.52-926.30) pg/mL, respectively (p <0.001). The median (min-max) NLR in mild and moderate COVID-19 was 2.18 (0.69-15.58) and 8.13 (2.24-30.90), respectively (p <0.001). The obtained cut-off values for IL-6 and NLR were >6.99 pg/mL and >4.18, with odds ratios of 29.29 and 26.19, respectively. A positive correlation was found between IL-6 and NLR and COVID-19 severity (r = 0.612; p <0.001). Conclusions: The results indicated that serum IL-6 levels and NLR are higher in severe COVID-19 than in mild COVID-19. Patients with IL-6 levels >6.99 pg/mL and NLR >4.18 are 29 and 26 times more likely to suffer from severe COVID-19, respectively. Serum IL-6 levels and NLR are strongly correlated with COVID-19 severity. Serum IL-6 levels correlate with NLR in COVID-19.