Serum Biomarkers of COPD—Reply

To the Editor: Ambade et al1 conducted an observational study to evaluate the potential serum biomarkers in subjects with COPD. The authors assessed superoxide dismutase-3, glutathione peroxidase, catalase, ceruloplasmin ferroxidase activity, C-reactive protein, and surfactant protein D in the serum of subjects with COPD and reported that ceruloplasmin ferroxidase activity and glutathione peroxidase are the most likely potential serum biomarkers in COPD. The study involved 96 stable COPD subjects in the study group and 96 subjects in the control group. In both groups, the number of males was higher than the number of females (male/female ratio of 73:23). Prior studies have reported that plasma glutathione peroxidase levels are significantly elevated in the plasma of females compared to males.2 Thus, the glutathione peroxidase activity measured by the Ambade et al1 is possibly attributable to the female population. It would have been interesting to see the glutathione peroxidase analysis of males and females separately for better understanding of glutathione peroxidase activity. Prior studies have reported that there is poor correlation of respiratory symptoms and lung function data in subjects with asthma.3 Ambade et al1 did not conduct any lung function tests on the control subjects because none of the control subjects had exhibited any respiratory symptoms, indicating incomplete subject information. Thus, the authors could have possibly measured the lung function parameters of controls as well for better understanding of the subject population involved in the study. Studies have also reported that smokers tend to have higher C-reactive protein levels compared with nonsmokers.4 It would have also been interesting to see a comparison within the healthy and COPD subgroups (ie, healthy nonsmokers versus healthy smokers and smokers in the COPD group versus nonsmokers in the COPD group). Last, the authors could have possibly correlated the ceruloplasmin ferroxidase activity and glutathione peroxidase data with lung function. This would have made the results easier to comprehend to better understand the disease pathogenesis and support the sensitivity of ceruloplasmin ferroxidase activity and glutathione peroxidase as effective biomarkers of COPD.