CHI3L1 and chronic obstructive pulmonary disease: Multivariate analysis showed that YKL-40 (HR 1.38; 95% CI: 1.11–1.72, p = 0.004), age (HR 1.05; 95% CI: 1.03–1.06, p < 0.0001), Severe COPD (HR 1.35; 95 CI: 1.03-1.76, p = 0.03) very severe COPD (HR 2.19; 95% CI: 1.60 - 2.99 < 0.0001), neutrophil granulocyte count (HR 1.05; 95% CI: 1.01-1.08, p = 0.01), and a smoking history of > 40 years (HR 1.38; 95% CI: 1.11-1.71, p = 0.003) were independent prognostic markers of OS.