Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

FRTIX
80315
FFRED
91819
Free Thyroxine Index (FTI), Serum
Clinical Information: The T-Uptake is an assessment of unsaturated thyroid binding proteins in
serum. The free thyroxine index is an estimate of the amount of circulating free thyroxine.
Useful For: T-Uptake (TU) and total thyroxine (T4) are used to estimate the amount of circulating free
T4. The estimate, or the free thyroxine index (FTI), is a normalized measurement that remains relatively
constant in healthy individuals and compensates for abnormal levels of binding proteins. Hyperthyroidism
causes increased FTI and hypothyroidism causes decreased values. TU results are changed by drugs or
physical conditions that alter the patient's thyroxine-binding globulin levels, or drugs that compete with
endogenous T4 and triiodothyronine (T3) for protein-binding sites. When serum contains high levels of
T3 and T4 as in hyperthyroidism, fewer unoccupied binding sites are available. Conversely, in
hypothyroidism, more binding sites are available.
Interpretation: The T-Uptake (TU) values used are interpreted in conjunction with total thyroxine
(T4) measurements. The free thyroxine index is calculated as: -FTI=(T4 concentration) x (% TU)/100
Reference Values:
T-UPTAKE
Males: 27-37%
Females: 20-37%
FREE THYROXINE INDEX
Males
3.0 suggest hyperthyroidism
Females
3.0 suggest hyperthyroidism
THYROXINE, TOTAL
Males
0-11 months: not established
1-9 years: 6.0-12.5 mcg/dL
10-23 years: 5.0-11.0 mcg/dL
> or =24 years: 5.0-12.5 mcg/dL
Females
0-11 months: not established
1-9 years: 6.0-12.5 mcg/dL
10-17 years: 5.0-11.0 mcg/dL
> or =18 years: 5.0-12.5 mcg/dL
Clinical References: 1. Whitley RJ, Meikle AW, Watts NB: Thyroid Function. In Tietz
Fundamentals of Clinical Chemistry. Fourth Edition. Edited by CA Burtis, ER Ashwood. Philadelphia,
EB Saunders Company 645-646, 1996 2. Klee GG, Hinz VS: The Ciba Corning ACS:180 Plus. In
Immunoassay Automation: An Updated Guide to Systems. Edited by DW Chan, Associated Press, New
York 63-102, 1996
Friedreich Ataxia Repeat Expansion Analysis - Unknown
Mutation
Reference Values:
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