Free thyroxine index is considered to be a reliable indicator of thyroid status in the presence of abnormalities in plasma protein binding. The free thyroxine index has generally been replaced by Free Thyroxine in the assessment of thyroid function, but is occasionally useful when a free T4 result is suspected of being anomalous.
Reference ranges for the free thyroxine index:
How to calculate the free thyroxine index?
The free thyroxine index (FTI) is determined by the following calculation:
Low levels are caused by hypothyroidism. Low results may also occur in hospitalised patients with non-thyroidal illness.
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High levels are caused by hyperthyroidism.
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5-Methyltetrahydrofolate, Adiponectin, Albumin/Creatinine Ratio, Random Urine, Anti-Thyroglobulin ab. (0-39), C-Peptide, Serum, Ceruloplasmin, Cyclic AMP, Plasma, Dihydrotestosterone (female), Dihydrotestosterone (male), Estimated Average Glucose (eAG), Free Androgen Index, Free testosterone, Free Testosterone, Direct (Female), Free Testosterone, Direct (Male), Free Thyroxine, Free Thyroxine Index, Fructosamine, Glucose, Glutamic Acid Decarboxylase, Hemoglobin A1c (HbA1c), Homocysteine, Insulin (Fasting), Insulin Antibody, Insulin-Like Growth Factor I (IGF-1), Iodine, Serum/Plasma, Parathyroid Hormone (PTH), Serum, Pregnenolone, Reverse T3, Serum, Sex Hormone-Binding Globulin (SHBG), T3, Free, T4, Free, T4, Total (Thyroxine), T7 Index, Testosterone, Testosterone (Female/Child), Testosterone, Serum (Female), Thyroglobulin, Thyroglobulin Antibodies (0 - 1 IU/L), Thyroid Peroxidase Antibodies (Anti-TPO Ab), Thyroid Stim Immunoglobulin, Thyroid-Stimulating Hormone (TSH), Thyrotropin Receptor Ab, Serum, Thyroxine-binding globulin, TBG, TMAO (Trimethylamine N-oxide), Total T3, Tri iodothyronine (T3) Uptake, Triiodothyronine, Serum