TABLE 6. Calculation of the Free Thyroxine Index (FT4
I) in Situations in Which the Serum TBG Concentration is Abnormal
|
|
|
|
|
High TBG Concentration |
Low TBG Concentration |
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|
Normal |
Normal TBG concentration |
(Pregnancy, BCP, Heredity) |
(Androgens, Heredity) |
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|
Values |
Euthyroid |
Hyperthyroid |
Hyperthyroid |
Euthyroid |
Hyperthyroid |
Hyperthyroid |
Euthyroid |
Hyperthyroid |
Hyperthyroid |
TT4(μg/dL) |
5–13 |
|||||||||
RT3U (%) |
25–35 |
10 |
15 |
5 |
15 |
15 |
8 |
4 |
10 |
2 |
FT4l |
5–13 |
32 |
38 |
20 |
20 |
30 |
15 |
40 |
50 |
30 |
Calculation of |
TT4× RT3U |
10.6 |
19 |
3.6 |
10 |
15 |
4 |
5.3 |
16.6 |
1 |
FT4I |
Mean normal RT3U |
10 × 32/30 |
15 × 36/30 |
15 × 20/30 |
15 × 30/30 |
15 × 30/30 |
8 15/30 |
4 40/30 |
10 50/30 |
2 30/30 |
TBG = thyroxine-binding globulin; TT4 = total thyroxine; RT3U
= resin T3 uptake; BCP = birth control pills
(Adapted from Mestman JH: Thyroid diseases in pregnancy.
Clin perinatol 12:651, 1985)