Three general approaches have been used to develop comparable FT4 and FT3 immunoassay methods: (i) two-step labeled-hormone; (ii) one-step labeled-analog; and (iii) labeled antibody. Guideline 13.

"A higher FT3/FT4 ratio was associated with an increased risk of developing NAFLD (OR 1.45) and greater severity of liver fibrosis (ORs 3.21–10.80), highlighting the potential role of thyroid hormones ...

These blood tests are effective in detecting abnormalities. FT3 and FT4 levels are also advised to know the levels of actual “effective” (non bound/free) thyroid hormones in circulation.” ...

When requested by the physician, the laboratory should be prepared to confirm a questionable result by performing a total hormone measurement or by re-measuring FT4 by a reference method that ...