Table 2 Laboratory findings and levothyroxine dose^a

NST

TSH (μU/ml) (median,range)

5.2 (0.1–356)

31.3 (0.8–260)

4.8 (0.1–356)

0.141

5.3 (0.1–356)

4.8 (0.5–11.9)

T4 (μg/dl)

6.8 ± 3.2

7.6 ± 4.1

6.7 ± 3.2

0.557

7.3 ± 1.9

6.7 ± 3.4

TSH > 20 μU/ml (n,%)

9 (13.8)

5 (62.5)

4 (7.0)

0.001*

0

9 (15.3)

T4 < 5 μg/dl (n,%)

12 (21.8)

1 (20.0)

11 (22.0)

1

0

12 (24.0)

Initial TSH (μU/ml) (median,range)

17.4 (0.8–100.0)

43.2 (1.0–100.0)

17.4 (0.8–100.0)

0.075

17.6 (0.8–199.9)

7.2 (5.0–42.0)

Initial fT4 (ng/dl)

1.2 ± 0.4

1.0 ± 0.4

1.2 ± 0.4

0.437

1.3 ± 0.2

1.1 ± 0.4

TSH > 20 μU/ml (n,%)

39 (49.4)

5 (55.6)

34 (48.6)

0.737

5 (55.6)

34 (48.6)

fT4 < 0.9 ng/dl (n,%)

22 (30.1)

2 (40.0)

20 (29.4)

0.634

0 (0)

22 (34.4)

TSH at off trial (μU/ml)

3.4 ± 3.0

5.7 ± 3.7

3.1 ± 3.7

0.295

3.8 ± 2.3

3.4 ± 3.1

Delayed TSH elevation (n,%)

20(25.0)

1(11.1)

19(26.8)

0.437

2(22.2)

18(25.4)

fT4 at off trial (ng/dl)

1.5 ± 0.2

1.5 ± 0.2

1.5 ± 0.2

0.796

1.4 ± 0.2

1.5 ± 0.2

Initial T4 dose (μg/kg/day)

11.2 ± 2.5

10.7 ± 2.5

11.4 ± 2.5

0.442

12.1 ± 2.0

11.2 ± 2.5

T4 dose (1 year) (μg/kg/day)

3.7 ± 1.4

4.3 ± 1.4

2.5 ± 1.4

< 0.001

3.3 ± 1.7

3.7 ± 1.3

T4 dose (2 years) (μg/kg/day)

3.1 ± 1.2

4.9 ± 1.2

3.5 ± 1.2

0.002

2.4 ± 0.3

3.2 ± 1.2

T4 dose at off trial (μg/kg/day)

2.8 ± 1.2

4.3 ± 1.2

2.9 ± 1.2

0.001

2.5 ± 0.7

2.8 ± 1.2

Off trial failure (n,%)

9 (11.3)

9 (100%)

0 (0%)

–

1(11.1)

8(11.3)