TY - JOUR T1 - Multicentre study to improve clinical interpretation of rheumatoid factor and anti-citrullinated protein/peptide antibodies test results JF - RMD Open JO - RMD Open DO - 10.1136/rmdopen-2021-002099 VL - 8 IS - 1 SP - e002099 AU - Lieve Van Hoovels AU - Bert Vander Cruyssen AU - Daniela Sieghart AU - Carolien Bonroy AU - Eszter Nagy AU - Rille Pullerits AU - Saša Čučnik AU - Charlotte Dahle AU - Ingmar Heijnen AU - Luca Bernasconi AU - Farid Benkhadra AU - Laura Bogaert AU - Stefanie Van Den Bremt AU - Ann Van Liedekerke AU - Geert Vanheule AU - Johan Robbrecht AU - Lucy Studholme AU - Claudine Wirth AU - Rüdiger Müller AU - Diego Kyburz AU - Christopher Sjöwall AU - Alf Kastbom AU - Rok Ješe AU - Boja Jovancevic AU - Emese Kiss AU - Peggy Jacques AU - Daniel Aletaha AU - Guenter Steiner AU - Patrick Verschueren AU - Xavier Bossuyt Y1 - 2022/03/01 UR - http://rmdopen.bmj.com/content/8/1/e002099.abstract N2 - Background Rheumatoid factor (RF) and anti-citrullinated protein/peptide antibodies (ACPA) are important biomarkers for diagnosis of rheumatoid arthritis (RA). However, there is poor harmonisation of RF and ACPA assays. The aim of this study was to refine RF and ACPA interpretation across commercial assays.Materials and methods Six total RF isotype-non-specific assays, 3 RF IgM isotype-specific assays and 9 ACPA immunoglobulin G assays of 13 different companies were evaluated using 398 diagnostic samples from patients with RA and 1073 disease controls.Results Using cut-offs proposed by the manufacturer, there was a large variability in diagnostic sensitivity and specificity between assays. Thresholds of antibody levels were determined based on predefined specificities and used to define test result intervals. Test result interval-specific likelihood ratios (LRs) were concordant across the different RF and ACPA assays. For all assays, the LR for RA increased with increasing antibody level. Higher LRs were found for ACPA than for RF. ACPA levels associated with LRs >80 were found in a substantial fraction (>22%) of patients with RA.Conclusion Defining thresholds for antibody levels and assigning test result interval-specific LRs allows alignment of clinical interpretation for all RF and ACPA assays.All data relevant to the study are included in the article or uploaded as supplementary information. ER -