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Biological markers can help to better identify a disease or refine its diagnosis. In the present study, the association between surfactant protein D (SP-D) and chronic obstructive pulmonary disease (COPD) was studied among subjects consulting for respiratory diseases or symptoms and was compared with C-reactive protein (CRP) and fibrinogen. A further aim of this study was to identify the optimal cut-off point of SP-D able to discriminate COPD patients. A case-control study including 90 COPD patients, 124 asthma patients and 180 controls was conducted. Standardized questionnaires were administered and lung function tests were performed. Biological markers were measured in blood samples according to standardized procedures. The association between SP-D and COPD was investigated using logistic regression models. Receiver-operating characteristic curves were used for threshold identification. SP-D levels above the median value were positively associated with COPD [adjusted odds ratio (OR)=3.86, 95% confidence interval (CI): 1.51-9.85, P=0.005). No associations with COPD or asthma were found for CRP or fibrinogen levels. Scores for COPD diagnosis in all COPD patients or ever-smoker COPD patients were identified (sensitivity, 76.4 and 77.8%; specificity, 89.3 and 88.5%, respectively). The results indicate that SP-D can differentiate COPD from other respiratory symptoms or diseases. Used with socio-demographic characteristics and respiratory symptoms, SP-D is able to discriminate COPD patients from controls, particularly among smokers.

Background: Surfactant protein D (SP-D), a promising systemic biomarker of chronic obstructive pulmonary disease (COPD) was never evaluated in the Lebanese population. Objective: The validity of serum SP-D as a biomarker for COPD, in comparison with C-reactive protein (CRP) and fibrinogen was investigated. Associations between SP-D levels and lung function tests and the value of combining SP-D and the Diagnosis Score of COPD (DS-COPD) for COPD diagnosis were also evaluated. Methods:90 COPD patients and 452 controls were recruited. Standardized questionnaires, lung function tests, COPD diagnosis (GOLD 2013), and blood collection were performed. Serum SP-D and CRP, and plasma fibrinogen levels were measured by ELISA. Associations between biological markers with lung function parameters and COPD were estimated by spearman correlation and logistic regression models respectively. Results: Median serum SP-D levels for COPD patients were 1510 ng/mL (from 986 to 2174 ng/mL). SP-D levels were positively associated with age and pack-years in controls (all p