Nonlinear Relationship Between Interleukin-6 and NT-proBNP at Admission in Hospitalized COVID-19 Patients

PURPOSE: Elevated levels of the inflammatory marker interleukin-6 (IL-6) and cardiac injury marker N-terminal pro-B-type natriuretic peptide (NT-proBNP) have been observed in patients with coronavirus disease 2019 (COVID-19). However, the relationship between IL-6 and NT-proBNP levels remains unclear. Therefore, we investigated the relationship between IL-6 and NT-proBNP levels in patients with COVID-19. PATIENTS AND METHODS: This was a cross-sectional study. Consecutive patients with COVID-19 were included herein. The independent and dependent target variables were the IL-6 and NT-proBNP levels, respectively, measured at baseline. Univariate and multivariate linear regression analyses and curve fitting were also performed. RESULTS: The average age of the 121 selected participants was 49.8 ± 15.8 years old, and 48.8% (59/121) were male. The estimated β value between Ln-transformed IL-6 and NT-proBNP was 0.28 (95% confidence interval [CI] 0.12–0.44, P = 0.001) in univariate logistic regression analysis and 0.09 (95% CI −0.04–0.21, P = 0.176) in the fully adjusted model. This relationship was nonlinear, with a point of 2.7, and the β values (and CIs) for the left (<2.7) and right (≥2.7) sides of the inflection point were −0.06 (95% CI −0.23–0.12, P = 0.534) and 0.77 (95% CI 0.18–1.37, P = 0.016) in the fully adjusted model, respectively. CONCLUSION: Our results suggest a nonlinear association between IL-6 and NT-proBNP levels. Higher IL-6 levels are associated with NT-proBNP in patients with COVID-19.