Thyroid function tests
Encyclopedia
Thyroid function tests is a collective term for blood test
s used to check the function of the thyroid
.
TFTs may be requested if a patient is thought to suffer from hyperthyroidism
(overactive thyroid) or hypothyroidism
(underactive thyroid), or to monitor the effectiveness of either thyroid-suppression or hormone replacement therapy. It is also requested routinely in conditions linked to thyroid disease, such as atrial fibrillation
and anxiety disorder
.
A TFT panel
typically includes thyroid hormones such as thyroid-stimulating hormone
(TSH, thyrotropin) and thyroxine
(T4), and triiodothyronine
(T3) depending on local laboratory policy.
(TSH, thyrotropin) is generally elevated in hypothyroidism and decreased in hyperthyroidism.
Reference ranges:
|Patient type>
Lower limit
Upper limit
Unit
>-
| Adults -
standard range
0.3, 0.4, 0.5, 0.6
3.0 , 4.0, 4.5, 6.0
Adults -
optimal range
0.3 , 0.5
2.0 , 3.0
| Infant
s 1.3
19
(Total T4) is generally elevated in hyperthyroidism
and decreased in hypothyroidism
. It is usually slightly elevated in pregnancy secondary to increased levels of thyroid binding globulin (TBG).
Reference ranges:
|Lower limit>
Upper limit
Unit
>-
| 4, 5.5
11, 12.3
| 60 140, 160
(Free T4) is generally elevated in hyperthyroidism
and decreased in hypothyroidism
.
|Patient type>
Lower limit
Upper limit
Unit
>-
|rowspan=2| Normal adult
0.7 ,0.8
1.4, 1.5, 1.8
| 9, 10, 12 18 , 23
|rowspan=2| Infant 0–3 d 2.0
5.0
| 26 65
|rowspan=2| Infant 3–30 d 0.9
2.2
| 12 30
|rowspan=2| Child/Adolescent
31 d – 18 y 0.8
2.0
| 10 26
|rowspan=2| Pregnant 0.5
1.0
| 6.5 13
(Total T3) is generally elevated in hyperthyroidism and decreased in hypothyroidism.
Reference ranges:
|Test>
Lower limit
Upper limit
Unit
>-
|rowspan=2| Total triiodothyronine
60, 75
175, 181
| 0.9 , 1.1 2.5 , 2.7
(Free T3) is generally elevated in hyperthyroidism and decreased in hypothyroidism.
Reference ranges:
|Patient type>
Lower limit
Upper limit
Unit
>-
|rowspan=2| Normal adult
0.2
0.5
| 3.1 7.7
|rowspan=2| Children 2–16 y 0.1
0.6
| 1.5 9.2
Calculated indices of free hormones
results in an increased total thyroxine and total triiodothyronine without an actual increase in hormonal activity of thyroid hormones.
Reference ranges:
|Lower limit>
Upper limit
Unit
>-
| 12
30
{| class="wikitable"
|Lower limit||Upper limit||Unit
|-
| 1.5|| 30 || pmol/L
|-
| 1 || 20 || μg/L
|-
|}
Reference ranges:
|Patient type>
Lower limit
Upper limit
Unit
>-
| Females
25
35
| In pregnancy 15
25
| Males 25
35
FTI is elevated in hyperthyroidism and decreased in hypothyroidism.
|Patient type>
Lower limit
Upper limit
Unit
>-
| Females
1.8
5.0
| Males 1.3
4.2
Blood test
A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a needle, or via fingerprick....
s used to check the function of the thyroid
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
.
TFTs may be requested if a patient is thought to suffer from hyperthyroidism
Hyperthyroidism
Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...
(overactive thyroid) or hypothyroidism
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...
(underactive thyroid), or to monitor the effectiveness of either thyroid-suppression or hormone replacement therapy. It is also requested routinely in conditions linked to thyroid disease, such as atrial fibrillation
Atrial fibrillation
Atrial fibrillation is the most common cardiac arrhythmia . It is a common cause of irregular heart beat, identified clinically by taking a pulse. Chaotic electrical activity in the two upper chambers of the heart result in the muscle fibrillating , instead of achieving coordinated contraction...
and anxiety disorder
Anxiety disorder
Anxiety disorder is a blanket term covering several different forms of abnormal and pathological fear and anxiety. Conditions now considered anxiety disorders only came under the aegis of psychiatry at the end of the 19th century. Gelder, Mayou & Geddes explains that anxiety disorders are...
.
A TFT panel
Test panel
A test panel is a predetermined group of medical tests as an aid in the diagnosis and treatment of disease.Test panels are typically composed of individual laboratory tests which are related in some way: by the medical condition they are intended to help diagnose , by the specimen type , by the...
typically includes thyroid hormones such as thyroid-stimulating hormone
Thyroid-stimulating hormone
Thyrotrophin-stimulating hormone is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid gland.- Physiology :...
(TSH, thyrotropin) and thyroxine
Thyroxine
Thyroxine, or 3,5,3',5'-tetraiodothyronine , a form of thyroid hormones, is the major hormone secreted by the follicular cells of the thyroid gland.-Synthesis and regulation:...
(T4), and triiodothyronine
Triiodothyronine
Triiodothyronine, C15H12I3NO4, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate....
(T3) depending on local laboratory policy.
Thyroid-stimulating hormone
Thyroid-stimulating hormoneThyroid-stimulating hormone
Thyrotrophin-stimulating hormone is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid gland.- Physiology :...
(TSH, thyrotropin) is generally elevated in hypothyroidism and decreased in hyperthyroidism.
Reference ranges:
>-
| Adults -
standard range
optimal range
| Infant
Infant
A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...
s
Total thyroxine
Total thyroxineThyroxine
Thyroxine, or 3,5,3',5'-tetraiodothyronine , a form of thyroid hormones, is the major hormone secreted by the follicular cells of the thyroid gland.-Synthesis and regulation:...
(Total T4) is generally elevated in hyperthyroidism
Hyperthyroidism
Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...
and decreased in hypothyroidism
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...
. It is usually slightly elevated in pregnancy secondary to increased levels of thyroid binding globulin (TBG).
Reference ranges:
>-
| 4, 5.5
| 60
Free thyroxine
Free thyroxineThyroxine
Thyroxine, or 3,5,3',5'-tetraiodothyronine , a form of thyroid hormones, is the major hormone secreted by the follicular cells of the thyroid gland.-Synthesis and regulation:...
(Free T4) is generally elevated in hyperthyroidism
Hyperthyroidism
Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...
and decreased in hypothyroidism
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...
.
>-
|rowspan=2| Normal adult
| 9, 10, 12
|rowspan=2| Infant 0–3 d
| 26
|rowspan=2| Infant 3–30 d
| 12
|rowspan=2| Child/Adolescent
31 d – 18 y
| 10
|rowspan=2| Pregnant
| 6.5
Total triiodothyronnine
Total triiodothyronineTriiodothyronine
Triiodothyronine, C15H12I3NO4, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate....
(Total T3) is generally elevated in hyperthyroidism and decreased in hypothyroidism.
Reference ranges:
>-
|rowspan=2| Total triiodothyronine
Triiodothyronine
Triiodothyronine, C15H12I3NO4, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate....
| 0.9 , 1.1
Free triiodothyronnine
Free triiodothyronineTriiodothyronine
Triiodothyronine, C15H12I3NO4, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate....
(Free T3) is generally elevated in hyperthyroidism and decreased in hypothyroidism.
Reference ranges:
>-
|rowspan=2| Normal adult
| 3.1
|rowspan=2| Children 2–16 y
| 1.5
Calculated indices of free hormones
- Free T4 index
- Free T3 index
Thyroxine-binding globulin
An increased thyroxine-binding globulinThyroxine-binding globulin
Thyroxine-binding globulin binds thyroid hormone in circulation. It is one of three proteins responsible for carrying the thyroid hormones thyroxine and 3,5,3’-triiodothyronine in the bloodstream. Of these three proteins, TBG has the highest affinity for T4 and T3, but is present in the lowest...
results in an increased total thyroxine and total triiodothyronine without an actual increase in hormonal activity of thyroid hormones.
Reference ranges:
>-
| 12
Thyroglobulin
Reference ranges:{| class="wikitable"
|Lower limit||Upper limit||Unit
|-
| 1.5|| 30 || pmol/L
|-
| 1 || 20 || μg/L
|-
|}
Thyroid hormone uptake
Thyroid hormone uptake (Tuptake or T3 uptake) is a measure of the unbound thyroxine binding globulins in the blood, that is, the TBG that is unsaturated with thyroid hormone. Unsaturated TBG increases with decreased levels of thyroid hormones. It is not directly related to triiodothyronine, despite the name T3 uptake.Reference ranges:
>-
| Females
| In pregnancy
| Males
Other protein binding tests
- Thyroid hormone binding ratio (THBR)
- Thyroxine-binding index (TBI)
Free thyroxine index
The Free Thyroxine Index (FTI or T7) is obtained by multiplying the total T4 with Tuptake. FTI is considered to be a more reliable indicator of thyroid status in the presence of abnormalities in plasma protein binding.FTI is elevated in hyperthyroidism and decreased in hypothyroidism.
>-
| Females
| Males
See also
- Reference ranges for blood tests#Hormones