MON-583 Functional Thyrotropin Receptor Antibodies in Pregnant Women with Thyroid Autoimmunity

Abstract

Background and Objectives: Thyrotropin receptor autoantibodies (TSHR-Ab) can cross through the placenta to the fetus and can cause fetal or neonatal hyper- or hypothyroidism. Patients with autoimmune thyroid disease (AITD) can also have TSHR-Ab, but data on the prevalence in pregnant women remain scarce. Therefore, the aim of the study was to determine the prevalence and activity (stimulatory, blocking, or both) of TSHR-Ab in pregnant women with AITD. Methods: Serum TSHR stimulating (TSAb) and blocking (TBAb) Ab were measured with cell-based reporter bioassays. Chinese Hamster Ovary cells express a chimeric TSHR and a cAMP response element (CRE)-dependent luciferase. TSAb was reported as percentage of specimen-to-reference ratio (cut-off SRR% <140%). Blocking activity was defined as percent inhibition of luciferase expression relative to induction with bovine TSH alone (<34% inhibition). Thyroid-related- hormones and autoantibodies were also measured. Results: A total of fifty pregnant patients with AITD were included; 46 were anti-thyroid peroxidase- (TPO) Ab positive and four were anti-thyroglobulin- (Tg) Ab positive. Serum levels (median, 25% and 75% percentiles) of TPO-Ab and Tg-Ab were 101 (69-185 IU/L, normal cut-off <34 IU/L) and 362 (185-1108 IU/L, cut-off 115 IU/L), respectively. Of the fifty patients, 40 (80%), nine (18%), and one (2%), were euthyroid, subclinical hypothyroid, and hyperthyroid, respectively. Serum levels of TSH were 0.19 mU/L (0.19-0.19 mU/L, normal range 0.27-4.2 mU/L), 4.9 (4.4-7), and 1.8 (1.4-2.3) for hyperthyroid, subclinical hypothyroid and euthyroid patients, respectively. Five females (10%) had low fT4 levels 11.2 (9.9-11.7 pmol/L, normal range 12-22 pmol/L) and one female had a high T4 level of 23.90 pmol/L. One hypothyroid patient with a high TSH value of 7.98 mU/L was positively tested in the TSAb bioassay, mean SRR value 422% and negatively tested in the TBAb bioassay, mean percent inhibition -44%. One euthyroid female patient with a serum TSH level of 2.12 mU/L was positive in the TBAb bioassay, mean inhibition 39% and negative in the TSAb bioassay, mean SRR value 91%. The remaining 48 female patients (96%) were tested negative for both TSAb and TBAb in the cell-based bioassays. Conclusions: The measurement of TSAb and TBAb adds interesting information in pregnant women with AITD. The clinical relevance of the blocking and stimulating antibodies remains to be correlated with the pregnancy outcome data.