Free thyroxine or free thyroxine index?
Free thyroxine (FT4) values determined by direct radio-immunoassay and the free thyroxine index (FTI) determined by indirect calculation were compared in 431 consecutive sera from patients with suspected thyroid dysfunction . Sensitivity and specificity were similar for both tests in the thyrotoxic, hypothyroid and euthyroid ranges with appropriate thyroid-binding globulin (TBG) concentrations. However, FT4 was superior to FTI in the euthyroid group with high concentrations of TBG, FT4 is therefore a useful alternative to FTI as a screening test for thyroid dysfunction, and is likely to be a better discriminator of thyroid status in patients with high TBG levels.
D005069:Evaluation Studies as Topic; D006801:Humans; D011863:Radioimmunoassay / Q000379:methods; D011933:Reagent Kits, Diagnostic; D013959:Thyroid Diseases / Q000097:blood; D013974:Thyroxine / Q000097:blood*
D011933:Reagent Kits, Diagnostic; D013974:Thyroxine