Comparison of rheumatoid factor of IgM, IgG and IgA isotypes with disease activity score 28 in patients of rheumatoid arthritis

Introduction/background: Rheumatoid factor (RF) is a widely used serological marker for the diagnosis of rheumatoid arthriris (RA). RF can be detected in up to 70 to 80% of RA patients and it is associated with disease activity, bone erosion, and disease outcome. RF is an autoantibody targeting the 'fraction crystallizable' (Fc) region of IgG antibodies and exists as IgA, IgG and IgM isotypes. The objective of this study was to compare the RF isotypes IgM, IgG and IgA with disease activity score 28 in rheumatoid arthritis patients. Materials and Methods: This was a descriptive study, which included 83 RA patients. Blood samples of the patients were collected from the Department of Rheumatology, Sheikh Zayed Hospital Lahore. The levels of different isotypes of RF i.e. IgM, IgG and IgA were determined by ELISA technique. Data was analysed by SPSS 20.0. Results: RF, IgM, IgG, and IgA isotype, was detected in 83%, 10%, and 40% of RA patients respectively. RF istoypes were compared with DAS28. There was no significant association between DAS 28 and RF IgM [Odd ratio (CI)] [0.5(0.07-3.18)], RF IgG [3.0(0.27-32.20)] and RF IgA [0.4(0.43-0.13)]. Disease duration was also compared with RF isotypes but no significant association found. There was no significant association between disease duration and RF IgM [Odd ratio (CI)] [1.4(0.46-4.86)], RF IgG [1.6(0.50-5.0)] and RF IgA [1.1(0.53-2.7)]. Conclusion: All the isotypes of RF were detected in RA patients. As a screening method for rheumatoid arthritis the IgM-RF is superior to other RF isotypes. RF titer may be valueable in estimation of disease activity and other inflammatory parameters in RA patients.