Christian Konrad, Germany
Thermo Fisher Scientific - Phadia GmbH Global Marketing AutoimmunityPresenter of 2 Presentations
A POTENTIAL RISK OF FALSE POSITIVE RESULTS WHEN UTILIZING PURIFIED HUMAN THYROID PEROXIDASE AS ANTIGEN IN ANTI-THYROID PEROXIDASE ANTIBODY TESTS
Abstract
Background and Aims
The quality of antigen is believed to be important to an in vitro diagnostic test. Protein purification from human/animal tissue and recombinant expression technology are the two commonly used techniques to acquire antigens. Purification of certain antigens does not completely eliminate the contamination with other cell components which might cause falsely elevated signals. Here, we aim to compare the way how antigens are purified and how this affects the results of routine samples.
Methods
First, we compared two commercially available tests for the measurement of anti-human thyroid peroxidase (TPO) antibodies. While one test applies TPO purified from human thyroid gland, the other applies recombinant human TPO. Various samples containing anti-TPO and/or anti-thyroglobulin (TG) antibodies were measured with both tests.
Results
When testing serum samples solely containing anti-TG antibodies, a strong signal was observed with the test applying purified TPO but not with the test that applies recombinant TPO. This indicates a potential interference of anti-TG antibodies on an anti-TPO diagnostic test that is dependent on the applied TPO antigen. To determine if this signal was indeed caused by anti-TG antibodies, these antibodies were depleted from samples containing anti-TG and/or anti-TPO antibodies by incubating the with soluble TG. Anti-TG-antibody-deplete samples, independent of anti-TPO antibody concentrations, showed a clear decrease in signal in the test using purified TPO, whereas the concentration remained unchanged when TPO was recombinant.
Conclusions
These results highlight that the antigen preparation significantly affects an antibody test’s performance. Test applying purified TPO could give false positive results when samples contain anti-TG antibodies.
COMBINING ANTI-CCP ANTIBODY AND RHEUMATOID FACTOR ISOTYPE SPECIFIC TEST RESULTS INCREASES THE DIAGNOSTIC CONFIDENCE OF RHEUMATOID ARTHRITIS
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.