Prognostic Value of Serum Interleukin-6 Level in Hypertensive Patients with COVID-19-Associated Pneumonia

Background. An interleukin-6 (IL-6) is a proinflammatory cytokine which plays an important role in COVID-19-associated hyperinflammation. 
Aim. This study aimed to assess the predictive ability of serum IL-6 levels for the development of severe/critical clinical conditions, a hypoxemic state requiring supplemental oxygen, and lethal outcomes in patients with COVID-19-associated pneumonia and arterial hypertension (AH). 
Materials and Methods. One hundred and thirty-five unvaccinated patients hospitalized for COVID-19-associated pneumonia were enrolled in the study. AH was diagnosed in 78.5% of cases. Pneumonia was confirmed radiologically. SARS-COV-2 as an etiological factor was confirmed by either PCR or ELISA. In addition to conventional laboratory tests, IL-6, ferritin, and soluble interleukin-2 levels were measured. 
Results. Among AH patients, the median levels of IL-6 were higher in non-survivors (95.1 [37.8 - 158.8] pg/mL) as compared to survivors (39.5 [13.6 - 81.1] pg/mL) (p=0.04). Among AH patients, the median serum level of IL-6 was 98.3 [37.8 - 158.8] pg/mL in critically ill patients, 41.7 [11.8 - 83.4] pg/mL in severely ill patients, 37.8 [13.6 - 74.4] pg/mL in moderately ill patients (p=0.051). The median serum level of IL-6 was lower at the time of discharge (6.5 [2.0 - 21.5] pg/mL) as compared to that on admission (43.2 [16.1 - 92.0] pg/mL) (p< 0.001). IL-6 level failed to predict severe/critical condition (AUC=0.59, p=0.13) and the need for supplemental oxygen (AUC=0.61, p=0.06); however, it might be used for the prediction of the lethal outcome (AUC=0.69, p=0.03). The cut-off value of IL-6 level for lethal outcome prediction of 91.0 pg/mL showed a sensitivity of 58.3% and a specificity of 78.7%. Patients with IL-6 levels > 91.0 pg/mL on admission had higher odds of lethal outcomes (OR = 4.87 [1.40 - 16.92], p=0.01). 
Conclusions. Serum IL-6 level on admission did not show significant predictive ability for severe/critical conditions and hypoxemic states requiring supplemental oxygen in AH patients. However, serum IL-6 levels on admission were higher in non-survivors and might be used for the prediction of lethal outcomes with a cut-off value of 91.0 pg/mL in AH patients.