Thyroid – Part 5 – Thyroxine Total, T4 Total
Sample
- This test is done on the serum of the patient.
- The sample is stable for 7 days at room temperature but refrigeration at 4 °C is preferred.
Precaution
- Avoid lipemic serum.
Indications
- This is done to assess thyroid function.
- it is done to diagnose thyroid diseases.
- This is also done to monitor the therapy.
Pathophysiology
- Thyroxine T4 forms by the combination of :
- diiodotyrosine + diiodotyrosine = Tetra Iodo Tyrosine (Thyroxine or T4).
- T4 makes most of the thyroid hormone because T3 is 10 %.
- 80% of the T4 is metabolized into:
- T3 = 35%
- rT3 = 45%
- 80% of the T4 is metabolized into:
- Most of the T4 is bound to thyroglobulin and albumin.
- T4 is pro-hormone with thyroglobulin binding (TBG).
- There is a very small fraction of free T4.
- Serum Total T4 = bound T4 + Free T4
- Thyroid glands have a major role in body function. T4 and T3 have a role in the growth, maturation of bone, and skeletal system.
- T3 is 3 to 8 times more metabolically active than T4 and is considered the active form of the thyroid hormone.
- It regulates body temperature.
- It has a role in the body’s metabolism of fats, carbohydrates, and proteins.
NORMAL
Source 1
T4 Total (T4)
Age | µg/dL |
Cord blood | 7.4 to 13.0 |
1 to 3 days | 11.8 to 22.6 |
1 to 2 weeks | 9.8 to 16.6 |
1 to 4 month | 7.2 to 14.4 |
4 to 12 month | 7.8 to 16.5 |
1 to 5 year | 7.3 to 15.0 |
5 to 10 year | 6.4 to 13.3 |
10 to 15 year | 5.6 to 11.7 |
Adult | Male = 4.6 to 10.5 Female = 5.5 to 11.0 |
>60 year | 5.0 to 10.7 |
Maternal serum 15 to 40 weeks | 9.1 to 14.0 |
Source 1
T4 Free (FT4)
Age | ng/dL |
Newborn 1 to 4 days | 2.2 to 5.3 |
Child (2 weeks to 20 Years | 0.8 to 2.0 |
Adult 21 to 87 years | 0.8 to 2.7 |
Pregnancy | |
1st trimester | 0.7 to 2.0 |
2nd and 3rd trimester | 0.5 to 1.6 |
- To converts SI unit x 12.9 = nmol/L
Source 2
T4 Total (T4)
Age | µg/dL |
1 to 3 days | 11.22 |
1 to 2 weeks | 10 to 16 |
1 o 12 months | 8 to 16 |
1 to 5 years | 7 to 15 |
5to 10 years | 6 to 13 |
10 to 15 years | 5 to 12 |
Adult | Male 4 to 12 Female 5 to 12 |
>60 years | 5 to 11 |
Source 2
T4 Free
- Newborn (0 to 4 days) = 2 to 6 ng/dL (26 to 77 pmol/L)
- Child 2 weeks to 20 years = 0.8 to 2.0 ng//dL
- Adult = 0.8 to 2.8 ng/dL (10 to 36 pmol/L)
- Infants 1 to 3 days = 11 to 22 µg/dL.
- Infants 1 to 4 months = 8 to 16 .µg/dL
- Child 1 to 5 years = 7 to 15 .µg/dL
- Child 10 to 15 years = 5 to 12 µg/dL.
- Adult Male = 4 to 12 µg/dL.
- Adult female = 5 to 12 µg/dL.
- adult > 60 years = 5 to 11 µg/dL.
The increased T4 level is seen in:
- Grave’s disease.
- Toxic thyroid adenoma.
- Struma ovarii.
- Acute thyroiditis.
The decreased T4 level is seen in:
- Hypothyroidism like:
- Cretinism.
- Myxedema.
- Surgical ablation.
- Failure of the hypothalamus.
- Protein-losing conditions like :
- Nephrotic syndrome.
- Renal failure.
- Iodine insufficiency.
- Cirrhosis.
- Cushing’s syndrome.
- Advanced cancers.
- Pituitary insufficiency.
The critical value of T4 Total:
- Newborn = <7 µg/dL
- Adult = <2 µg/dL
Please see more details in Free T4 and thyroid function.