What is T3, T4, TSH?
The Thyroid Profile Total is a group of tests that are done together to detect or diagnose thyroid diseases. It measures the levels of the following three hormones in the blood: Thyroid Stimulating Hormone (TSH), Thyroxine (T4) - Total and Triiodothyronine (T3) - Total.
Note : On the day of test, those who are on thyroid medications, should take them in the same time and dosage as prescribed by the doctor.
It should not be held for the test.
Why is T3, T4, TSH done?
The Thyroid Profile Total test is done:
- To diagnose any suspected thyroid disease (Hypothyroidism or Hyperthyroidism)
- To monitor treatment in patients with thyroid diseases
- To investigate the cause of infertility
What does T3, T4, TSH Measure?
The Thyroid Profile Total test measures the levels of the following three hormones in the blood:
Thyroid Stimulating Hormone (TSH)
Thyroxine (T4) - Total
TriIodothyronine (T3) - Total
The thyroid gland (a small, butterfly-shaped gland located in front of the neck) secretes the following hormones:
- Triiodothyronine (T3)
- Thyroxine (T4)
Thyroid Stimulating Hormone (TSH), also called Thyrotropin is a hormone secreted into the blood by the Pituitary gland (a gland present in the brain)). It tells your thyroid gland to make and release the thyroid hormones (T3 & T4) into your blood. The thyroid gland uses the iodine gained from food to make the thyroid hormones.
The thyroid hormones are essential for growth and metabolism. If the thyroid gland produces very high amounts of T3 and T4 hormones, you may experience symptoms like weight loss, rapid heartbeat, tremors, sweating, anxiety, increased sensitivity to heat, etc. and this is known as Hyperthyroidism.
The decreased production of thyroid hormones (T3 and T4) results in Hypothyroidism which may lead to weight gain, fatigue, slow heart rate, increased sensitivity to cold, depression, dry and thin hair, etc.
There is a feedback system in the body to maintain stable amounts of the thyroid hormones (T3 and T4) in the blood. When the levels of thyroid hormone decrease, the pituitary gland is stimulated to release TSH. High TSH in turn increases the release of T3 and T4 thyroid hormones from the thyroid gland and vice-versa.
T3 and T4 circulate in the blood in two forms:
1) Bound form - It is bound to proteins present in blood and this prevents it from entering the body tissues. The three main proteins in the blood that the thyroid hormones are bound to are albumin, transthyretin and Thyroxine-binding globulin (TBG), also called Thyroid hormone Binding Globulin (THBG).
2) Free form - It enters the body tissues where it is needed
The total T3 or total T4 includes both bound and free forms circulating in the blood. Hence, thyroid hormones can be measured as Free T3, Total T3, Free T4, and Total T4.
The total T3 and total T4 levels can be affected by the amount of protein available in the blood to bind to them.
Interpreting T3, T4, TSH results
Interpretations
T3 (Triiodothyronine), Total Reference Range(s)
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<1 Month
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Not established
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1-23 Months
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117-239 ng/dL
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2-12 Years
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105-207 ng/dL
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|
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13-20 Years
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86-192 ng/dL
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>20 Years
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76-181 ng/dL
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T4 (Thyroxine), Total
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4.5-12.0 mcg/dL
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Thyroid Stimulating Hormone (TSH) Reference Range(s)
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Premature Infants (28-36 Weeks)
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1st Week of Life
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0.20-27.90 mIU/L
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Term Infants (>37 Weeks)
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Serum or Cord Blood
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1.00-39.00 mIU/L
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1-2 Days
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3.20-34.60 mIU/L
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3-4 Days
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0.70-15.40 mIU/L
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5 Days-4 Weeks
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1.70-9.10 mIU/L
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1-11 Months
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0.80-8.20 mIU/L
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1-19 Years
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0.50-4.30 mIU/L
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≥20 Years
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0.40-4.50 mIU/L
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Pregnancy
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First Trimester
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0.26-2.66 mIU/L
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Second Trimester
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0.55-2.73 mIU/L
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Third Trimester
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0.43-2.91 mIU/L
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Table 1. Interpretation of the Thyroid Profile Test results
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TSH
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T4
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T3
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INTERPRETATION
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Elevated
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Normal
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Normal
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Mild (subclinical) hypothyroidism
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Elevated
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Low
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Low or normal
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Hypothyroidism
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Low
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Normal
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Normal
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Mild (subclinical) hyperthyroidism
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Low
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Elevated or normal
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High or normal
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Hyperthyroidism
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Low
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Low or normal
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Low or normal
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Nonthyroidal illness; hypothyroidism due to the disease involving the pituitary gland
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Normal
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Elevated
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Elevated
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Thyroid hormone resistance (Impaired sensitivity to thyroid hormone)
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- Low T4 and T3 along with high TSH level indicates hypothyroidism. The most common cause of hypothyroidism is Hashimoto thyroiditis
- High T4 and T3 along with low TSH indicate hyperthyroidism. The most common cause of hyperthyroidism is Grave’s disease
- Normal thyroxine (T4) and T3 along with high TSH usually indicates mild or subclinical hypothyroidism
- Normal T3 and T4 along with low TSH indicates mild or subclinical hyperthyroidism
Note: TSH levels show circadian variation (fluctuates during the 24-hour cycle), reaching peak levels between 2 - 4 am and are at a low between 6-10 pm.
Reference Range(s) may vary from lab to lab.
Tests Included (3 tests)
