Comparison of TPOAb assays in early pregnancy
R Henley1, AB Parkes2, L Taylor2, R John1 & JH Lazarus2
The presence of thyroid peroxidase antibodies (TPOAb) is a marker of autoimmune thyroid disease and, when present in early pregnancy, is predictive of postpartum thyroiditis. In the course of undertaking the Controlled Antenatal Thyroid Screening Study we have taken the opportunity to measure TPOAb in a large number of samples from 1116 weeks gestation by 3 different assays.
The assays were (1) an in-house ELISA; (2) Bayer ADVIA Centaur anti-TPO assay, and (3) Abbott AXSYM anti-TPO assay.
Of 923 samples measured by in-house and Bayer 50 were abnormal by both assays, 14 abnormal by in-house and 11 by Bayer. The correlation between the two assays was 0.711. In 836 samples (a different group) assayed by in-house and Abbott, 90 were positive to both assays, 32 by in-house alone and 23 by Abbott alone. The correlation was 0.727. The correlation between Bayer and Abbott assays in 688 samples was only 0.2 possibly because there were very few positives in this group by either technique.
It is concluded that, while the performance of each method was satisfactory up to 5% of samples may give different results depending on the assay. Further exploration of the antigen antibody interaction in this regard is warranted.