Macro-TSH Interference in Thyroid Function Testing: a Case Report and Literature Review

TSH testing is crucial for the diagnosis and treatment of thyroid diseases. Accurate TSH levels are essential for determining thyroid function status, guiding treatment plans, and monitoring disease progression; this case emphasizes the importance of identifying and excluding the influence of interfering factors in thyroid function testing. Interfering factors, such as the presence of macro-TSH, can lead to clinical misdiagnosis and mis-treatment. The mechanism and clinical significance of macro-TSH formation are not yet fully elucidated, and the combination of anti-TSH antibodies with TSH may be the main cause of macro-TSH formation. All macro-TSH patients show positive anti-TSH antibodies, but not all patients with positive anti-TSH antibodies will form macro-TSH. When thyroid function test results do not match clinical symptoms or the changes in TSH, FT3, and FT4 do not conform to the rules, it is necessary to exclude the presence of test interferents such as macro-TSH. In this case, the normalization of TSH levels after treatment with the PEG6000 precipitation method confirmed the presence of macro-TSH in the patient's serum, thus avoiding unnecessary treatment.