TNF and chronic obstructive pulmonary disease: However, the ELISA results showed that median serum levels of TNF‐α were similar in COPD smokers (1.24 pg/ml, 0.73–1.82), COPD non‐smokers (1.22 pg/ml, 0.74–1.24) and healthy smokers (0.89 pg/ml, 072–3.31).