COMBINING ANTI-CCP ANTIBODY AND RHEUMATOID FACTOR ISOTYPE SPECIFIC TEST RESULTS INCREASES THE DIAGNOSTIC CONFIDENCE OF RHEUMATOID ARTHRITIS
- Christian Konrad, Germany
Abstract
Background and Aims
Analyzing patient samples for anti-CCP autoantibodies and rheumatoid factor (RF) IgM represents a pivotal aid in the diagnosis of rheumatoid arthritis and has been included in the 2010 ACR/EULAR rheumatoid arthritis classification criteria. In the early phases of RA, its differential diagnosis from other diseases can be difficult. Some studies suggested an increase in diagnostic confidence by additionally testing for RF IgA and combining test results. We aimed to contribute to the ongoing scientific debate about the combination of test results by analyzing samples from early RA patients for anti-CCP, RF IgM and RF IgA autoantibodies.
Methods
A sample cohort of 100 rheumatoid arthritis patients (symptoms less than two years) and 149 disease controls were analyzed for the above mentioned serological markers with the respective EliATM tests.
Results
In this study, anti-CCP, RF IgM and RF IgA autoantibodies were measured in 62%, 62% and 50% of early RA patients at a specificity of 95.3%, 90.6% and 91.9%, respectively. 56 % of the RA samples but only 1.3% of the disease controls were positive for both anti-CCP and RF IgM leading to a positive likelihood ratio (LR(+)) of 41.72 and a positive predictive value (PPV) of 0.97. Triple positivity for all three autoantibodies was detected in 45% of the RA samples and only 0.7% of the controls. The calculated LR(+) and PPV was 67.1 and 0.98, respectively.
Conclusions
The combination of anti-CCP, RF IgM and RF IgA autoantibody testing can provide a higher diagnostic confidence of RA than testing for either marker alone.