An improved and simplified method for the detection of thyroid hormone autoantibodies (THAA) in serum

High prevalence of thyroid hormone autoantibody and low rate of thyroid hormone detection interference

Objective

Thyroid hormone autoantibody (THAb) is a common antibody in autoimmune disease and can interfere with the detection of thyroid hormone (TH). There was no research reporting the prevalence of THAb in Chinese and the rate of THAb interfering with TH detection.

Methods

We collected 114 patients with autoimmune thyroid disease (AITD) (Hashimoto's thyroiditis, 57 cases; Graves’ disease, 57 cases), 106 patients with nonthyroid autoimmune diseases (NTAID), and 120 healthy subjects. According to the presence or absence of thyroid antibodies, patients with NTAID were divided into two groups: NTAID‐AITD and NTAID groups. Radioimmunoprecipitation technique was used to detect THAb in all subjects. TH was detected on Abbot and Roche platforms in patients with positive THAb.

Results

The prevalence of THAb was 22.8% in Hashimoto's thyroiditis and 45.6% in Graves’ disease. The prevalence of THAb in AITD group was lower than that in NTAID or NTAID‐AITD groups (34.2% vs. 61.5%, p = 0.014; 34.2% vs. 71.3%, p < 0.01). Among total 98 patients with positive THAb, TH levels of 9 patients were falsely elevated (9.18%).

Conclusion

The prevalence of THAb in AITD patients was lower than that in NTAID patients. Although THAb had a high frequency in various autoimmune diseases, the prevalence of THAb interfering with TH detection was only 9.18%.

Antibody interference in thyroid assays: a potential for clinical misinformation

Measurements of thyrotropin and of total and free thyroxine and triiodothyronine are widely used diagnostic methods for thyroid function evaluation. However, some serum samples will demonstrate a nonspecific binding with assay reagents that can interfere with the measurement of these hormones. Several recent case reports have described the presence of such interferences resulting in reported abnormal concentrations of thyroid hormones inconsistent with the patient’s thyroid state. Circulating thyroid hormone autoantibodies, described in thyroid and nonthyroid disorders, are an important class of interference factor and can bind to hormone tracers used in various immunoassays. Two additional categories of interfering antibodies may particularly interfere within two-site immunoassays for thyrotropin. These include heterophile antibodies, especially human anti-mouse antibodies, and rheumatoid factors, which can cause interferences by immunoglobulin aggregation and (or) cross-linking of both capture and signal antibodies. Here we review the nature of these disturbances; their occurrence, prevalence, and detection; and the clinical consequences of the failure to recognize such interference.

Thyroid hormone autoantibodies in patients with Graves' disease: effect of anti-thyroid drug treatment

We examined the effects of anti-thyroid drug treatment on serum autoantibodies against thyroid hormones (thyroid hormone autoantibodies, THAA), thyroglobulin (Tg) and thyroid peroxidase (TPO) in patients with Graves' disease by measuring each autoantibody level before and after treatment. Six patients among 40 untreated patients with Graves' disease had anti-thyroxine (T4) antibodies. One patient had both anti-T4 and anti-triiodothyronine (T3) antibodies. Thus the prevalence of THAA in untreated Graves' disease was 7 out of 40 (17.5%). Changes in T4-Ab levels after treatment varied. In five cases (cases 3-7) levels decreased 4-7 months after treatment. However, in the other two cases levels fluctuated 1, 3, 6 and 12 months after treatment. None of the previously THAA-negative patients became positive after treatment. Anti-Tg antibody (Tg-Ab) was positive in 34 out of 40 (85%) untreated cases and its level decreased in both THAA positive and negative patients after treatment. Anti-thyroid peroxidase antibody (TPO-Ab) was positive in 32 of the 40 (80%) untreated Graves' patients and its level significantly decreased after treatment. Our findings suggest that treatment with anti-thyroid drugs does not produce THAA in Graves' disease.

Evaluation of thyroid function in patients with thyroid hormone autoantibodies

Serum free thyroxine (FT4) levels were measured in patients with Hashimoto's thyroiditis and Graves' disease who were seropositive for thyroid hormone autoantibodies. The methods used were equilibrium dialysis/radioimmunoassay (FT4 by equilibrium dialysis, Nichols Institute) and FT4 analog radioimmunoassay (Amerlex MFT4) before and after treatment of sera with 12.5% polyethylene glycol (PEG). Furthermore, FT4 measurement in the PEG-treated sera was done using two other analog radioimmunoassays (DPC FT4 Kit and N-FT4 Corning). Serum thyrotropin (TSH) concentration before and after i.v. infusion of thyrotropin releasing hormone (TRH) was measured in five cases of Hashimoto's thyroiditis and four cases of Graves' disease with thyroid hormone autoantibodies. Although FT4 determination by analog tracer radioimmunoassays showed unusually high values for the hormone, results obtained by an equilibrium dialysis/radioimmunoassay method showed compatible values with basal TSH. Furthermore, FT4 concentrations measured with Amerlex MFT4 after treatment of sera with 12.5% PEG, correlated well with the values obtained by equilibrium dialysis/radioimmunoassay (r = 0.98, P < 0.001). Similar results were obtained with two other analog FT4 radioimmunoassays after treatment of sera with PEG. These results indicate that real FT4 values in patients with thyroid hormone autoantibodies are compatible with basal TSH concentrations. The presence of thyroid hormone autoantibodies per se does not affect the control mechanism of the hypothalamo-pituitary-thyroid axis. It was concluded that measurement of basal TSH as well as FT4 values by either equilibrium dialysis/radioimmunoassay or analog radioimmunoassays after PEG treatment provides clinicians with valid information for assessment of the precise status of thyroid function in patients with thyroid hormone autoantibodies.

Thyroid hormone autoantibodies (THAA) in three sisters: a four-year follow up

We have found three sisters who had thyroid hormone autoantibodies (THAA) in serum. Two of them were hypothyroid due to Hashimoto's thyroiditis. They were treated with synthetic thyroxine (T4) (Case 1) or T4 and triiodothyronine (T3) (Case 2). The other sister (Case 3) was euthyroid throughout the investigation period. Changes in the titers of THAA, antithyroglobulin (Tg) antibodies as well as in the concentrations of thyrotropin (TSH), and total and free thyroid hormones (T3, T4, FT3, and FT4) in sera from each patient were examined for four years. A significant positive correlation was observed between titers of THAA and anti-Tg antibodies in both Case 1 (anti-T3 and anti-T4) and 2 (anti-T4). On the other hand, a significant negative correlation between titers of anti-T3 and anti-Tg antibodies was observed in Case 3. These results suggest that antigen of THAA might be Tg in Case 1 and 2 and mechanism(s) of the production of THAA of Case 1 might be different from that of Case 1 and 2 in terms of their antigen or immune recognition of Tg.

A 3,3',5-triiodothyronine autoantibody (IgG, lambda) in a case of Hashimoto's thyroiditis

A 19-year-old Japanese woman with Hashimoto's thyroiditis appeared to be hypothyroid by clinical and laboratory criteria. However, the serum levels of total T3 and free T3 as measured by solid-phase radioimmunoassay were not compatible with the clinical features and other laboratory data, therefore the presence of serum T3 autoantibodies was suspected. Gel filtration analysis (Sephacryl S-300) of acid-treated serum trace-labeled with 125I-T3 revealed binding to high and intermediate molecular fractions, indicating that the T3 binding autoantibody may have been IgM and IgG. The antibody, however, was identified as IgG class and lambda type by immunoprecipitation and immunoelectrophoresis/autoradiography. The T3 binding autoantibody did not show antigenic cross-reactivity with T4 as far as we know from experiments. The affinity and the binding capacity of the antibody for T3 were estimated 6.4 X 10(6) l/mol and 9.1 X 10(-9) mol/l, respectively.