Indirect Measurement of Free T4 or Free T3 (2)	

	The results are usually related to a standard reference serum and are used as a ratio of the results of the unknown serum to the reference serum for calculation of the free thyroxine index (FTI) (Fig. 15.13). Thyroid hormone binding tests are often incorrectly and misleadingly referred to as ‘T3 tests’. They utilise 125I-T3 but are not measure of total or free T3; they are an indirect measure of TB capacity and allow adjustment of total T4 concentrations in altered TBG status.

See also:
• Thyroid Hormone Transport