Introduction: Structure, importance and incidence and clinical role of macro-TSH not clarified in thyroid diseases. Aim: This study was undertaken to determine the incidence and biological role of macro-TSH in patients with Hashimoto's thyroiditis. Method: Blood samples taken from patients with Hashimoto's thyroiditis were screened for the presence of macro- TSH with the polyethylene glycol method and confirmed with protein G agarose absorption test and gel filtration chromatography. Stimulatory capacity of macro-TSH was measured by CHO cells bio-Assay. Patients were treated with L-Thyroxine (mean 66.5 μg/day) and half of them with selenium (mean 60 μg/day), respectively. Results: 880 patients (728 female, aged 44.8 yr) with Hashimoto's thyroiditis was involved in the study. Macro-TSH was found in the serum of 41 patients (4.6%), the mean TSH 185.4 ± 35 IU/l was before PEG precipitations and after 5.55 ± 1.8 IU/l. Titre of anti-TPO proved to be 445 ± 51 IU/l and gradulally decreased to 212 ± 51 IU/l after one year therapy. Both the precipitation, protein G absorption and gel chromatography supported the presence of anti-TSH antibody in the macro-TSH complex. Stimulatory capacity of macro-TSH on CHO bio-Assay was not proved. The macro-TSH was detected in the selenium not treated group for 18 ± 3.2 months, selenium-Treated for 12 ± 1.9 months. Conclusion: It is concluded that anti-human TSH autoantibodies are a major components of macro-TSH and may cause diagnostic and therapeutical difficulties. The PEG precipitation is a suitable screening method for detection of macro-TSH. Selenium is able to decrease of anti-TPO antibodies and macro-TSH, respectively. When the TSH level is greater than 40.0 IU/l, without the signs of hypothyroidism, the presence of macro-TSH is to be considered.
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