Correlation Between Anti-Carbamylated Protein Antibody And Interstitial Lung Disease Secondary To Rheumatoid Arthritis

Objective:This study aims to detect relative level of anti-carbamylated protein（anti-Car P）antibody in the blood of patients with rheumatoid arthritis secondary to interstitial lung disease（RA-ILD）,and compare with that of patients with rheumatoid arthritis（RA）alone.We also investigate the correlation between anti-Carp antibody and RA-ILD,aiming to summarize the clinical features of RA-ILD and its common TCM syndrome types.Methods:A total of 39 RA patients and 37 RA-ILD patients admitted in the Respiratory Department and Rheumatism Department of The Fourth Clinical Medical College of Xinjiang Medical University were recruited.Venous blood sample（5 m L）of each patient on the 2^ndday of admission after overnight fasting was collected for measuring anti-Carp antibody level by enzyme-linked immunosorbent assay（ELISA）.In addition,clinical data of them were recorded,including anti-cyclic peptide containing citrulline（anti-CCP）,rheumatoid factor（RF）,erythrocyte sedimentation rate（ESR）,C-reactive protein（C-RP）,and disease activity score 28（DAS28-ESR）.Interstitial lung disease（ILD）in RA patients was examined by high-resolution computed tomography（HRCT）,and the degree of lung injury was assessed by the Warrick score for the evaluation of chest CT scan.The correlation between anti-Carp antibody and RA-ILD was statistically analyzed.Finally,the common TCM syndrome types of RA-ILD were summarized based on the findings obtained from the four methods of diagnosis.Results:There were significant differences in the age（P<0.001）and course of disease（P=0.009）between RA-ILD group and RA group.The anti-Carp antibody level in RA-ILD group was significantly higher than that of RA group（P<0.001）.In RA-ILD group,anti-Carp antibody level was positively correlated to RF（r=0.393,P=0.016）,ESR（r=0.364,P=0.027）and CRP（r=0.518,P=0.001）.Moreover,anti-CCP antibody level was positively correlated to RF in RA-ILD group（r=0.371,P=0.024）.The anti-Carp antibody level in RA-ILD group was also positively correlated to the Warrick score（r=0.370,P=0.026）.ROC curves were depicted based on the anti-Carp antibody level in both groups,and the positive rate,sensitivity,specificity and cut-off value were 81.3%,75.7%,82.10%and17.45 U/ml,respectively.Among 37 RA-ILD patients,11（29.7%）with the deficiency of both Qi and Yin,9（24.4%）with the syndrome of Qi deficiency of lung and kidney,7（18.9%）with the pattern of phlegm-heat congesting the lung,3（8.1%）with the pattern of phlegm turbidity obstructing the lung,4（10.8%）with the deficiency of lung Qi,and 3（8.1%）with the syndrome of endogenous heat due to Yin deficiency.The most common TCM syndrome of RA-ILD was the deficiency of both Qi and Yin.Anti-Carp antibody level was statistically significant in RA-ILD patients with different TCM syndromes.Conclusions:When the anti-Carp antibody level in RA patients is higher than17.45U/ml,it has the diagnostic potential of RA-ILD with higher sensitivity and specificity for assessing the disease activity and lung damage.Triple-positive anti-Carp antibody,anti-CCP antibody and ESR suggests the active stage of RA.RA patients aged62±13 years old or those with more than 10 years of disease course should be alert to the risk of RA-ILD.The subpleural line in the early-stage lung CT suggested the early stage of RA-ILD.At this time,the use of drugs that may induce lung injuries should be avoided.Moreover,lung function should be regularly monitored to adjust medications in time,thus alleviating the process of pulmonary fibrosis.