THU0097 VALUE OF ANTIBODIES AGAINST ACETYLATED PEPTIDES FOR THE CLASSIFICATION OF PATIENTS WITH EARLY ARTHRITIS
Authors: Lorena Rodríguez-Martínez, Holger Bang, Laura Nuño, Diana Peiteado, Ana Ortiz, Alejandro Villalva, Dora Pascual-Salcedo, Ana Martínez-Feito, Alejandro Balsa, Isidoro González-Álvaro, Antonio Gonzalez
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> Patients with rheumatoid arthritis (RA) achieve the best response when they receive adequate treatment as soon as possible. This fact motivated the modification of the classification criteria by the ACR and the EULAR in 2010 to enable early detection. One of the changes is the increased weight conferred to the autoantibodies: rheumatoid factor and anti-citrullinated protein antibodies. As these antibodies are not present in all patients, other antibodies could provide similar information. In this regard, the antibodies that recognize an acetylated peptide from mutated vimentin (Anti-Acetylated Peptide Antibodies or AAPA) stand out (1). <h3>Objectives:</h3> We aimed to evaluate the AAPA predictive value at the baseline visit for the classification of early arthritis patients. <h3>Methods:</h3> A total of 438 patients with available samples and information were randomly selected from two early arthritis clinics. The AAPA were determined in baseline sera as previously described (1). Two peptides were included, one acetylated at a lysine (anti-AcLys) and the other at an ornithine (anti-AcOrn) and considered either individually or combined. The sensitivity, specificity, predictive positive (PPV) and negative (PNV) values and the AUC of the ROC curve were assessed. Logistic regression was also applied adjusting for age, sex, the centre of origin, anti-CCP, and RF. The study was approved by the ethics committee of the Hospital Universitario La Paz, the Hospital Universitario La Princesa, and Autonómico de Galicia. <h3>Results:</h3> The AAPA at baseline were sensitive and specific for the classification of the patients fulfilling RA criteria (46.8%) at the end of the 2-year follow-up (table 1). Specifically, the anti-AcOrn antibodies were slightly more sensitive and specific than the anti-AcLys ones. The two and their combination showed a conserved specificity for the seronegative patients, but a lower sensitivity than for the seropositive ones. Consequently, the PPV for the seronegative patients was low, although the NPV was high. In the same vein, the AUC was insufficient for the seronegative patients. The regression analysis including the anti-CCP and RF revealed a significant contribution of the anti-AcOrn antibodies (OR = 2.1, 95% CI = 1.1 – 4.0, P = 0.02), but not of the anti-AcLys antibodies. On the other hand, the inclusion of the AAPA in the classification resulted in an increase in sensitivity of 5.4% at the cost of a 13.7% lower specificity, which is an improvement over the anti-carbamylated protein antibodies. Supported by grants PI17/01606 and RD16/0012/0014 of the Instituto de Salud Carlos III (Spain) that are partially financed by the FEDER <h3>Conclusion:</h3> The AAPA show high specificity and sensitivity for RA in early arthritis patients. However, their contribution to RA classification is minor once RF and the anti-CCP antibodies have been considered. But nevertheless, AAPA supports the drive to close the diagnostic gap in this early disease phase and to increase the likelihood of successful therapy. <h3>References:</h3> [1] Juarez, M, et al. Ann Rheum Dis. 2016; 75:1099-1107 <h3>Disclosure of Interests:</h3> Lorena Rodríguez-Martínez: None declared, Holger Bang Employee of: Dr. Bang is employee of the diagnostic company Orgentec Diagnostika., Laura Nuño: None declared, Diana Peiteado: None declared, Ana Ortiz: None declared, Alejandro Villalva: None declared, DORA PASCUAL-SALCEDO Grant/research support from: Pfizer, Speakers bureau: Pfizer, Abbvie, Takeda, ANA MARTÍNEZ-FEITO: None declared, Alejandro Balsa Grant/research support from: Abbvie, Pfizer, Novartis, BMS, Nordic, Sanofi, Consultant for: Abbvie, Pfizer, Novartis, BMS, Nordic, Sanofi, Sandoz, Lilly, Paid instructor for: Pfizer, Speakers bureau: Pfizer, Novartis, UCB, Nordic, Sanofi, Sandoz, Lilly, Isidoro González-Álvaro: None declared, Antonio Gonzalez: None declared