Total T4 (Total Thyroxine)

Clinical definition of the Total Thyroxine (T4) test
T4 is one of the hormones produced by the thyroid gland. In blood, T4 is either free (not bound) or protein- bound (bound to thyroxin- binding globulin). Total T4 test is used to diagnose hyperthyroidism and hypothyroidism.

Why is the Total Thyroxine (T4) test done?
To help evaluate thyroid gland function; to help diagnose hypothyroidism or hyperthyroidism; to screen for hypothyroidism in newborns

What are the common signs/symptoms when the Total Thyroxine (T4) test is done?
Excessive amounts of T4 in the blood results in symptoms associated with hyperthyroidism such as:

  • Nervousness
  • Tremors of the hands
  • Weight loss
  • Insomnia
  • Puffiness around dry, irritated eyes
  • Eyes cannot move normally
  • Increased heart rate
  • Anxiety

Insufficient amounts of T4, show symptoms associated with hypothyroidism and a slowed metabolism, such as:

  • Weight gain
  • Dry skin
  • Fatigue
  • Constipation
  • Irregular menstruation

What should I do before the Total Thyroxine (T4) test?

Specimen type

Specimen collection procedure

Preparatory instructions before the test *

Serum

(Blood Sample)

Venipuncture

(Collection of blood from a vein, usually from the arm)

No Fasting Required.

No other special preparations required

*Subjects suffering from any illness or on oral or injectable medications are advised to consult their physician prior to requesting any tests or procedures.

How do I interpret my Total Thyroxine (T4) test results?

Gender

Reference Range*

Male/Female

3.2 - 12.6  µg/dL

Male (Hypothyroid)

Below 4.5 ug/dL

Male (Hyperthyroid)

Above 13 ug/dL

Children

Boy

Girl

1 - 7 days

7.7 - 66

4.8 - 67

8 - 15 days

21 - 66

13.6 - 83

1 - 3 yrs

4.8 - 10.6

6.5 - 13.3

4 - 6 yrs

6.2 - 11.7

7.8 - 12.6

7 - 8  yrs

6.3 - 14.0

7.6 - 12.4

9 - 10 yrs

4.7 - 15.6

5.8 - 14.3

11  yrs

6.3 - 11.1

6.2 - 12.5

12 yrs

7.2 - 10.9

6.5 - 9.0

13 yrs

5.1 - 10.2

5.2 - 9.5

14 yrs

6.2 - 9.6

5.2 - 9.5

15 yrs

5.1 - 9.9

5.7 - 9.5

16 yrs

5.5 - 9.6

5.9 - 9.0

17 yrs

4.6 - 9.8

6.2 - 8.7

18 - 19 yrs

4.7 - 9.2

4.8 - 9.0

‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’

Diseases/conditions related to the Total Thyroxine (T4) test

  • Hypothyroidism
  • Hashimoto's disease
  • Graves disease
  • Iodine-induced hyperthyroidism
  • Subacute or chronic thyroiditis
  • Toxic multinodular goiter
  • Trophoblastic disease
  • Thyroid cancer
  • Goiter
  • Thyroid Disorders
  • Acute thyroiditis
  • Cretinism
  • Cirrhosis
  • Malnutrition
  • Hepatitis

Other tests related to the Total Thyroxine (T4) test

  • TSH
  • T3
  • Thyroid Antibodies
  • T7 (T3 and T4)

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T4 (Total)

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