Value of serum and induced sputum surfactant protein-D in chronic obstructive pulmonary disease

Aim: In the present study, we aimed to investigate the correlation between SP-D in serum and induced sputum and severity of COPD. Methods: 20 healthy subjects older than 40 years of age with at least 10 pack- year smoking history (group 1), 20 stage I-II COPD patients (group 2) and 20 stage III-IV COPD patients (group 3) were enrolled to the study. All subjects performed pulmonary function tests and C-reactive protein (CRP) and blood SP-D levels measured. Induced sputum samples were obtained to determine induced sputum SP-D level. COPD patients were followed up for exacerbation for 6 months. Results: Serum SP-D levels of group 3 were highest and and induced sputum SP-D levels of group 2 were lowest among three groups. However, there were no statistically significant differences among three groups ( p>0.05). SP-D levels of induced sputum decreased in patients with high number of cigarette pack-year, whereas serum SP-D levels increased in these patients (p<0.05). Induced sputum SP-D levels of COPD patients receiving inhaler corticosteroid treatment were higher than patients who were not receiving inhaler corticosteroid treatment (p<0.05). An inverse correlation between serum SP-D levels and FEV 1 (L,%) was found and there was a positive significant correlation between the serum SP-D levels and exacerbation frequency in 6-month follow up period in our study (p<0.05). Conclusion: Our study demonstrates adverse effects of smoking on local SP-D levels. Low levels of local SP-D in the group of current smokers, who were not receiving inhaler corticosteroid treatment indicate the importance of airway inflammation in COPD pathogenesis.