To enhance the diagnostic power, a combined ROC curve comprising all correlative factors with statistical significance (season; COPD history; TO-A; percentages of CD4+ T, CD8+ T, and DNT cells; and levels of CRP; LDL-C; Na+; and FCa2+, as well as T lymphocyte percentage and TC level) was designed, with a remarkably improved prediction power (sensitivity = 75.61%, specificity = 76.83%; AUC = 0.8711, p < 0.0001; R2 = 0.4235) than those of the respective factors (Table 5 and Figure 1). Here, CD4 is linked to chronic obstructive pulmonary disease.