Free T3 is measured as a second line test when the TSH result indicates a thyroid function disorder (e.g. thyrotoxicosis or hypopituitarism).
No known common methodological interferences. Any influence that might affect the binding behaviour of the binding proteins can alter the result of the fT3 tests (e.g. drugs, NTIs (Non-Thyroid-Illness) or patients suffering from FDH (Familial Dysalbuminemic Hyperthyroxinemia). Autoantibodies to thyroid hormones can interfere with the assay. Binding protein anomalies seen with FDH (familial dysalbuminemic hyperthyroxinemia), for example, may cause values which, while characteristic of the condition, deviate from the expected results.
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