Human autoimmune thyroid disease A mechanistic update

Interference of anti-T4 autoantibodies in the single step free T4 radioimmunoassays

The thyroid hormone profile of a hypothyroid patient, with moderate sized diffuse goiter and history of exogenous thyroid hormone therapy, was found to be highly ambiguous. The total as well as free T4 levels were consistently high (out of range) with suppressed T3 (total and free) and elevated thyrotropin levels. We incubated the serum with the radio-iodine labelled T4 and observed that the patient's serum bound about 50.5% of the total radioactivity resulting in 85.3% interference in the radioimmunoassay. On resolving the serum proteins by cellulose acetate electrophoresis, the radioactivity was detected in the gamma globulin band. The protein profile showed mildly raised levels of IgG. Therefore it was established that the patient's serum carried T4 reactive antibodies (IgG) which were interfering in the immunoassays. Elevated anti-thyroid microsomal antibodies were also present in the patient's serum. The anti-T4 antibodies were highly specific for T4 and did not show any cross reactivity with the T3 or its analogues used in the estimation of free T3. We stripped the serum by precipitating the immunoglobulins and were successful in estimating the levels of free T4 in the stripped serum by single step radioimmunoassy.

Interference of anti-T3 autoantibodies in the measurement of total and free T3 in serum

A case of anti-trilodothyronine autoantibodies is presented in this report. The thyroid hormone profile of a hypertensive patient, with multinodular goiter and history of exogenous thyroid hormone therapy, was found to be highly ambiguous. The total as well as free T3 levels were consistently high (out of range) whereas the T4 (total and free) values were always within normal limits. The thyrotropin was found to be partially suppressed. Very low T3-Uptake indicated some kind of interference in the immunoassays. We incubated the sera with the radio-iodine labelled T3 and observed that the patient's serum bound about ten times more radioactivity than a control run in parallel. On further resolving the serum proteins on cellulose acetate electrophoresis, the radioactivity was detected in the γ-globulin band. Therefore it was established that the patient's serum carried the antibodies reactive with T3 which were interfering in the immunoassays. Elevated anti-thyroid microsomal antibodies were also present in the patient's serum. The anti-T3 antibodies were highly specific for T3 and did not show any cross reactivity with the T4 or its analogues used in the estimation of free T4.

Thyroid autoantibodies and pregnancy outcomes

Autoimmune thyroid disease has been associated with several adverse pregnancy outcomes. Increased risk of spontaneous miscarriage and placental abruption in women with thyroid antibodies has been confirmed in multiple studies. However, benefit of intervention and treatment of autoimmune thyroid disease in otherwise euthyroid pregnant women has not been sufficiently studied. The data on the association of thyroid antibodies and recurrent pregnancy loss or preterm birth are conflicting and a statistically significant association has not been shown in large studies. At present time, routine screening and treatment of autoimmune thyroid disease in euthyroid pregnant women is not warranted.

Thyroid autoimmunity, infertility and miscarriage

Thyroid autoimmunity (TAI), infertility and miscarriage are currently issues of extreme interest that have attracted the attention of many investigators. Several papers have been published, focusing on women of childbearing age that include healthy women, women with recurrent miscarriage and those undergoing assisted conception. Most of these studies show a significant association between the presence of thyroid autoantibodies, infertility and a higher miscarriage rate. The underlying pathogenetic mechanisms, which might explain the association between TAI and infertility, remain speculative given the scarce information from animal models and from in vitro data addressing the potential effects of TAI on fertility. Adequate levels of circulating thyroid hormones are of primary importance for normal reproductive function and inadequate delivery of triiodothyronine to granulosa and stromal cells may disrupt normal female reproductive function. With regards to the association between TAI and miscarriage, a close relationship has been largely confirmed in recent studies. The aim of this review is to present the relevant information published so far in the literature regarding TAI and miscarriage in euthyroid female individuals.

Influence of thyroid autoimmunity and maternal age on the risk of miscarriage

OBJECTIVES

Recently, studies have shown an association between antiperoxidase for the detection of thyroid autoimmunity (TAI) and abortion. Another point to be considered is the association of high risk of abortion and maternal age. The aim of the present study was to evaluate if the association between TAI and miscarriage could also be verified whether a population of unselected pregnant young women who normally present a low risk of miscarriage.

MATERIALS AND METHODS

We studied 534 pregnant women, by determining their serum thyroid antiperoxidase antibodies (TPO-Abs), thyrotropin (TSH) and free thyroxine (fT4) levels. Our end point was the pregnancy loss or live birth.

RESULTS

Age ranged from 12 to 49 years (mean +/- S.D.; 23.5 +/- 5.9). Of 534 women, 29 (5.4%) were TPO-Ab positive. TSH levels were significantly higher in TPO-Ab-positive women compared with TPO-Ab negative women (median; 1.9 versus 1.1; P = 0.001). Elevated TSH levels were found in 13.8% (4 of 29) of the TPO-Ab-positive women compared with only 2.4% (12 of 505) in the TPO-Ab-negative women. There were no significant differences in fT4 levels in relation with autoimmunity and risk of miscarriage. The overall risk of miscarriage was 2.4% (13 of 534). Risk of miscarriage was significantly higher among women older than 35 years (7.7%), TPO-Ab positive (10.3%) and presenting high levels of TSH (12.5%). These factors remained independently associated with the risk of miscarriage in full multivariate analysis.

CONCLUSIONS

We conclude that TAI is independently associated with is a higher risk of miscarriage in a population of unselected pregnant presenting a low risk of miscarriage.

Antithyroid antibodies do not affect pregnancy outcome in women undergoing assisted reproduction

The purpose of this study was to determine the association of antibodies to thyroglobulin and thyroid peroxidase and pregnancy outcome in women undergoing assisted reproductive techniques. The study included three centres and retrospectively evaluated patient sera for antithyroid antibodies, then related the results to pregnancy outcome. Enzyme-linked immunosorbant assays for thyroglobulin and thyroid peroxidase antibodies were performed using two different commercially available kits. Controls included 200 healthy women of reproductive age. Women (n = 873) who were undergoing assisted reproductive techniques for pelvic adhesions, endometriosis, ovarian dysfunction, or unexplained/other were included. All women utilized a standard regimen of gonadotrophin releasing hormone agonist down-regulation followed by ovulation induction. Embryos were cultured for 3 days, at which time embryo transfer occurred. Statistical analysis utilized the two-tailed Fisher's exact test. Antithyroid antibodies were positive in 143 of 873 (16.4%) women undergoing assisted reproductive techniques while 29 of 200 (14.5%) normal controls were positive (not significant). Deliveries were achieved in 396 of 730 (54.2%) of women who had no thyroid antibodies versus 78 of 143 (54.5%) of women who had thyroid antibodies (not significant). No difference in biochemical pregnancies (not significant) or clinical pregnancy losses (not significant) were detected. Antithyroid antibodies were found no more frequently in women undergoing assisted reproductive techniques than in normal controls. There were no differences in pregnancy outcome based on antithyroid antibody positivity in women undergoing assisted reproductive techniques. These data do not support the testing or treatment for antithyroid antibodies of women undergoing assisted reproductive techniques.

Increased prevalence of antithyroid antibodies identified in women with recurrent pregnancy loss but not in women undergoing assisted reproduction

OBJECTIVE

To assess the prevalence of antibodies to thyroglobulin and thyroid peroxidase (or microsomal) in women with recurrent pregnancy loss and women undergoing assisted reproductive techniques (ART) compared with healthy controls.

DESIGN

Retrospective, two-centered study.

SETTING

University-affiliated private patient centers.

PATIENT(S)

Included were 700 women with a history of two or more consecutive pregnancy losses, 688 women with a history of infertility who were undergoing ART, and 200 healthy, reproductive-aged female controls.

INTERVENTION(S)

Blood was collected before ART cycles, frozen, and assayed.

MAIN OUTCOME MEASURE(S)

Standardized ELISAs were used to measure antithyroid antibodies and TSH levels. Statistical analysis was performed with use of the two-tailed Fisher's exact test.

RESULT(S)

Antithyroid antibodies were identified in 29 of 200 (14.5%) of controls and 158 of 700 (22.5%) of women with recurrent pregnancy loss and 132 of 688 (19.2%) of women undergoing ART. Less than 20% of the women with antithyroid antibodies were clinically hypothyroid.

CONCLUSION(S)

Antithyroid antibodies are identified more frequently in women with recurrent pregnancy loss than in controls but not in women undergoing ART. These autoantibodies may be markers of autoimmune activation and have been associated with an increased risk of pregnancy loss and postpartum thyroid disease.