[Significance of anti-carbamylated protein antibodies in patients with rheumatoid arthritis-associated intersitial lung disease].

OBJECTIVE: To evaluate the value of anti-carbamylated protein (CarP) antibody in the diagnosis of rheumatoid arthritis-associated intersitial lung diseas (RA-ILD).
METHODS: Clinical and laboratory data and serum samples of patients with RA between December 2017 and June 2019 in Department of Rheumatology, General Hospital of Ningxia Medical University were collected. The patients were subclassified as RA-ILD and RA-without ILD based on computed tomography scans of the chest, Enzyme 1inked immunosorbent assay (ELISA) was used to assess anti-CarP antibody in the serum of each group. The occurrence of ILD and other laboratory indexes were analyzed. Comparison of measurement data between the 2 groups was performed by two independent sample t-test or Mann-Whitney U nonparametric test, while the count data were compared by Chi square test; Receiver operating characteristic curve (ROC) was drawn to determine the cut-off value of anti-CarP antibody to RA-ILD diagnosis and to analyze its diagnostic efficacy.
RESULTS: The anti-CarP antibody level in the RA-ILD group was 21.14 (12.29, 29.75), which was significantly higher than that in the RA-without ILD group 11.6 (6.66, 19.05) (P=0.000). The difference was statistically significant (P<0.05). The positive rate of anti-CarP antibody in RA-ILD group (53%) was significantly higher than that in RA-without ILD group (16%) (P<0.05); There was no significant differences in the levels of rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP) between the two groups (P>0.05). The age and disease activity score (DAS28) in the RA-ILD group were significantly higher than those in the RA-withhout ILD group (P<0.05). The proportion of men and smoking in the RA-ILD group was higher than that in the RA-without ILD group, but the difference was not statistically significant. The ROC curve showed that the anti-CarP antibody had a cut off value of 20.56 U/mL, with the sensitivity of 53.50%, and specificity of 84.20%, the area under the ROC curve were 0.76. Spearman correlation analysis showed that rheumatoid factor (RF) and age were positively correlated with anti-CarP antibody (r=0.172, P=0.043; r=0.200, P=0.006). Anti-CarP antibody level was not associated with the DAS28 score, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), anti-CCP antibody, swollen joint count, and tender joint count (P>0.05).
CONCLUSION: The anti-CarP antibody level in RA-ILD patients is higher than that in RA-without ILD, suggesting that anti-CarP antibody may have a role in the development of RA-ILD.