Thyroxine - Age Variation in Serum

Age
T4 (mcg/dl) Mean
(SD)
Birth (cord blood)
12.7
(3.4)
24-48 hours
16.5
(2.4)
7 days
14.1
(3.0)
1-12 months
10.8
(2.3)
1-6 years
9.3
(2.0)
7-12 years
8.6
(1.9)
13-17 years
8.0
(1.9)
18-30 years
8.1
(1.7)

It is not known whether the data above are approximately normally distributed. It is suggested that a z value be calculated for a given T4 result from the table. [z = (T4 result - mean)/standard deviation]. The probability that z should be between -2 and +2 would then be approximately 0.95 for a normal distribution.

Reference: Fisher DA. Thyroid Physiology and Function tests in Infancy and Childhood in Werner, SC,
and Ingbar SH, editors: The Thyroid, 4th Ed., New York, 1978 Harper and Row, p. 382.


Serum T4 Concentration in Premature and Term Infants

 
Estimated gestational age (wk)
 
30-31
32-33
34-35
36-37
Term
Cord          
Mean
6.5*
7.5
6.7<
7.5
8.2
SD
1.0
2.1
1.2
2.8
1.8
n
3
8
18
17
37
 
12-72 hr          
Mean
11.5=
12.3=
12.4=
15.5<
19.0
SD
2.1
3.2
3.1
2.6
2.1
n
12
18
17
15
6
 
3-10 days          
Mean
7.7=
8.5=
10.0=
12.7<
15.9
SD
1.8
1.9
2.4
2.5
3.0
n
7
8
9
9
29
 
11-20 days          
Mean
7.5<
8.3=
10.5
11.2
12.2
SD
1.8
1.6
1.8
2.9
2.0
n
5
11
9
9
8
 
21-45 days          
Mean
7.8=
8.0=
9.3<
11.4
12.1
SD
1.5
1.7
1.3
4.2
1.5
n
11
17
13
5
5
 
46-90 days
(30 to 37 weeks)
      
Mean
  
9.6
    
10.2
SD
  
1.7
    
1.9
n
  
16
    
17
 

*P<0.05

<P<0.005}for the comparison of premature vs. term infants (t test).

=P<0.001

It is not known whether the data above are approximately normally distributed. It is suggested that 
a z value be calculated for a given T4 result from the table.  [z = (T4 result - mean)/standard 
deviation]. The probability that z should be between -2 and +2 would then be approximately 0.95 for a 
normal distribution.

Reference: Cuestas RA. Thyroid function in healthy premature infants, J. Pediatrics 92:963 (1978).