The higher, than expected, levels of inflammation in comparators may be attributed to the age of the participants and potential presence of subclinical disease in some comparators despite being free from occult respiratory, cardiovascular disease, or inflammatory conditions.34 COPD is characterized by low-grade inflammation; both CRP and fibrinogen are acute phase proteins produced by the liver and have been associated with disease severity in COPD. Here, CRP is linked to chronic obstructive pulmonary disease.