Background/Purpose: In recent years several studies suggest that first order stratification of RA should be based on the presence or absence of rheumatoid factor (RF) and anti-citrullinated peptide antibodies (ACPA) in sera [1,2]. Both RF and ACPA can be detected in the sera of some patients years before the onset of arthritis [3,4]. It has been shown that in patients presenting with undifferentiated arthritis, both RF and ACPA are stable biomarkers, and rarely change over the course of the first year of disease [5]. The longitudinal course of these important and commonly used biomarkers in established RA over a prolonged period of time is less clear. The objective of our study was to determine the rates of seroconversion for RF and ACPA, in patients with RA over an extended period of follow up.

Methods: 155 subjects (111 Female, Age Range 31-90 years) with RA meeting ACR/EULAR classification criteria were included. All subjects had assessments of RF at diagnosis and at their most recent clinical follow up and 58 had assessments of ACPA at diagnosis and most recent follow up.

Results: Subjects were assessed for RF for a median of 4.49 years (IQR 1.92-8.40) following the sample taken at diagnosis. Seroconversion for RF was observed in 15/94 (16.0%) of patients. Where RF was detectable at diagnosis, it became undetectable in the sera of 10/61 (16.4%). Subjects were assessed for ACPA a median of 1.90 years (IQR 0.63-3.54) following the sample taken at diagnosis. Seroconversion was not observed in any of the 25 patients who were negative for ACPA at diagnosis. Where ACPA was detectable at diagnosis, it became undetectable in the sera of 1/35 (2.9%).

Conclusion: In addition to being more specific for RA, ACPA offers the advantage over RF of being more stable over time. Our data suggests little merit in repeat testing of ACPA over time, and suggests the index result can be used to appropriately sub-classify the RA phenotype. References: 1 Willemze A, Trouw LA, Toes RE, et al. The influence of ACPA status and characteristics on the course of RA. Nat Rev Rheumatol 2012;8:144–52. doi:10.1038/nrrheum.2011.204 2 Klareskog L, Catrina AI, Paget S. Rheumatoid arthritis. Lancet 2009;373:659–72. doi:10.1016/S0140-6736(09)60008-8 3 Nielen MMJ, van Schaardenburg D, Reesink HW, et al. Specific autoantibodies precede the symptoms of rheumatoid arthritis: A study of serial measurements in blood donors. Arthritis Rheum 2004;50:380–6. doi:10.1002/art.20018 4 Rantapaa-Dahlqvist S, de Jong BA, Berglin E, et al. Antibodies against cyclic citrullinated peptide and IgA rheumatoid factor predict the development of rheumatoid arthritis. Arthritis Rheum 2003;48:2741–9. doi:10.1002/art.11223 5 Mjaavatten MD, van der Heijde DM, Uhlig T, et al. Should Anti-citrullinated Protein Antibody and Rheumatoid Factor Status Be Reassessed During the First Year of Followup in Recent-Onset Arthritis? A Longitudinal Study. J Rheumatol 2011;38:2336–41. doi:10.3899/jrheum.110234

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-longitudinal-stability-of-the-ra-biomarkers-rf-and-acpa-in-classifying-ra-subtypes-over-extended-follow-up/