Free Thyroxine Index Normal Range. The free thyroxine index has generally been replaced by free thyroxine in the assessment of thyroid function, but is occasionally useful when a free t4 result is suspected of being anomalous. In abnormal cases like hyperthyroidism, the value is greater than 8.0 µg%.
The free thyroxine index (fti) is determined by the following calculation: Fti = thyroxine (t4) / thyroid binding capacity. 1 the normal range for the free thyroxine index (ft 4 i) is given as 1 to 4 ng per 100 ml,.
Similarly, in the case of hypothyroidism, the serum value falls below 3 µg%.
A low tsh and low ft4 or fti indicates hypothyroidism due to a. Replacement thyroxine therapy is often associated with increased t4 and free t4 and normal concentrations of t3. In abnormal cases like hyperthyroidism, the value is greater than 8.0 µg%. Free thyroxine is often more useful than total thyroxine in assessing thyroid function.