A POTENTIAL RISK OF FALSE POSITIVE RESULTS WHEN UTILIZING PURIFIED HUMAN THYROID PEROXIDASE AS ANTIGEN IN ANTI-THYROID PEROXIDASE ANTIBODY TESTS
- Christian Konrad, Germany
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.