CX3CL1 and chronic obstructive pulmonary disease: Results: Compared to severe COPD with COVID-19 patients, circulating biomarkers of CX3CL1 (453.3 vs. 305.3 pg/mL, p<0.01) and D-dimer (1231.8 ng/mL vs. 680 ng/mL, p<0.01) were significantly elevated in critical illness participants. The C indices of inflammatory biomarkers CX3CL1 and D-dimer were 0.78 and 0.68, respectively. Furthermore, the prolonged illness of COPD patients with COVID-19 was associated with circulating inflammatory biomarkers of CX3CL1 (p=0.021) and D-dimer (p=0.041).