COVID-SErology in Rheumatoid Arthritis (COVID-19)

Due to the Covid-19 worldwide outbreak, fragile patients with immune diseases, notably rheumatoid arthritis (RA), have to be even more specifically and carefully followed-up. However, it has been shown that false postive serological results often occured while detecting antibodies directed against SARS-CoV-2 in patients with positive rheumatodoid factor (RF). The investigators propose here to investigated this issue. Therefore, the investigators will test three different immunoassays on this specific population. The investigators aim to establish these assays specificity and the levels of RF for which there is a risk of anti-SARS-CoV-2 false positivity and thus ensure a better follow-up of RA patients. The RF isotype will be analysed to determine whether there is a correlation and the impact of the presence of anti-CCP (citrullinated cyclic antipeptide antibodies) will be studied and assessed.