INTRODUCTION: Rheumatoid factor (RF), despite its limitations, is still the most applied serological marker for diagnosis of early rheumatoid arthritis (RA). Sensitivity, specificity, correlation with prognosis and radiological progression, as well as variation over time of serotypes titers IgG, IgM and IgA, are yet controversial. OBJECTIVE: To evaluate the pattern of the different RF serotypes (IgG, IgM, and IgA) in serial evaluations during the first 36 months after RA diagnosis and their correlation with occurrence of radiographic erosions. PATIENTS AND METHODS: Forty patients with diagnosis of RA (less than 12 months of symptoms) were evaluated during 3 years of follow-up. Titers of RF serotypes were analyzed by ELISA at the initial evaluation and after 12, 24 and 36 months of follow-up. A mixed-effect regression model was applied, considering the presence of radiographic erosions as outcome (annual radiography of hands and wrists, feet and ankles). RESULTS: At the initial evaluation, 30%, 42.5% and 50% of the patients were positive for IgG, IgA and IgM RF, respectively. The titers of IgA and IgM RF were higher for patients who had radiographic erosions during the follow-up period (10-220 IU/dL versus 0 to 10 IU/dL in patients without erosions, P < 0,05). The titers of IgM and IgG RF remained unchanged over the three years of follow-up. On the other hand, there was a positive linear increasing trend for titers of IgA RF (P = 0.0013) only in the group with radiographic erosions. CONCLUSION: 1) Search of RF serotypes IgA and IgG does not increase the frequency of RF positivity and therefore it does not contribute to the RA diagnosis; 2) IgM RF stability observed over time does not justify repeated requests of RF during RA follow-up; 3) higher titers of IgA and IgM RF are observed in more severe patients, with radiographic erosions; 4) IgA RF presents a clearly distinct behavior in patients with or without radiographic erosions, which may have implications for pathophysiology and prognostic evaluation of the disease.
rheumatoid factor; serotypes; early rheumatoid arthritis; diagnosis; prognosis
