To investigate the serum level of surfactant protein D (SP-D) in the patients with stable phase of plateau chronic obstructive pulmonary disease (COPD) and its relationship with frequent exacerbator phenotype, lung function, and systemic inflammation.

A total of 150 patients living on plateau for generations with stable COPD hospitalized in West China Hospital of Sichuan University from May 2016 to December 2017 (the COPD group) and 67 healthy controls (the control group) were enrolled in this study. The clinical data of the two groups were collected including their age, gender, body mass index (BMI), the smoking index and the lung function indicators including the forced expiratory volume in one second (FEV₁), FEV₁%, FEV₁/the forced vital capacity (FVC)%. Venous blood was taken to measure the SP-D, C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factorα (TNF-α). The differences in the serum SP-D, CRP, IL-6, and TNF-α were analyzed between the Han and Tibetans in the stable phase of COPD and between the two groups. Correlation analyses were made between the serum SP-D and pulmonary function and systemic inflammation, CAT (COPD testing scores) and modified British Medical Research Council (mMRC) scores in the patients with stable COPD. Statistical multivariate regression analysis was made for the SP-D of the patients in the stable phase of COPD and its relationship with the Han and Tibetans. In ROC analysis, P<0.05 was considered as statistical significance.

The SP-D of the COPD group was higher than that of the control group (12 524±8 796 vs. 9 288±5 640 ng/L, P<0.05), The inflammation indexes, such as CRP [0.5 (2.3) in the COPD group vs. 2 (2.5) in the control group, P<0.05], IL-6 [2.3(2.2) in the COPD group vs. 1.1(1.4) in the control group, P<0.05], and TNF-α(5.5±2.7 in the COPD group vs. 7.8±6.7 in the control group, P<0.05) had significant differences between the two groups. The SP-D of the COPD group was positively correlated with the CAT score (r=0.498, P<0.05), mMRC score (r=0.512, P<0.05), and the levels of inflammatory factors such as CRP (r=0.369, P<0.05), IL-6 (r=0.454, P<0.05) and TNF-α (r=0.529, P<0.05), and negatively correlated with the lung function indexes such as FEV₁% (r=-0.404, P<0.05) and FEV₁/FVC% (r=-0.171, P<0.05). There was no significant difference in serum SP-D and inflammatory factors of CRP, IL-6 and TNF-α between the Han and Tibetan patients in the stable COPD patients (P>0.05). The multivariate regression analysis showed that P>0.05 was found in the SP-D of the COPD patients, but no indicator related to the stable phase was found. In the ROC statistics, the threshold of SP-D was 9 303.5, the sensitivity was 0.576, and the specificity was 0.616. SP-D had certain diagnostic values for the diagnosis of COPD in the stable phase.

Elevated serum SP-D can reflect the systemic inflammatory levels, is helpful to assess the degree of pulmonary function, and diseases the changes in the patients with high-altitude COPD. It has a certain effect on the prediction and evaluation of plateau COPD.