T3 T4 TSH

Thyroid Function Test panel measures the levels of total thyroxine T-4, total triiodothyronine T-3 and thyroid stimulating hormone (TSH) in blood.

What is Thyroid Stimulating Hormone?

The thyroid stimulating hormone is a pituitary hormone that stimulates the thyroid gland to produce triiodothyronine (T3) and thyroxine (T4) hormones. These hormones help to control the rate at which energy is used in almost every tissue in the body.

What are T4 and T3 Hormones?

Thyroxine (T4) and Triiodothyronine (T3) which are secreted into the blood binds reversibly to the transport proteins like thyroxine-binding globulin (TBG), thyroxine binding prealbumin (TBPA), and albumin. Remaining unbound T4 and T3 circulates freely in blood and used by the body. This freely circulating Thyroxine (T4) and Triiodothyronine (T3) are known as Free Thyroxine FT-4 and Free triiodothyronine FT-3.

What are Hyper and Hypothyroidism?

This test is performed to measure whether the thyroid gland is hyperactive (Hyperthyroidism) or underactive (Hypothyroidism). Hyperthyroidism is a condition in which thyroid gland produces excessive hormones. This condition may cause signs and symptoms such as weight loss, irritability, sweating, and irregular heartbeats. Hypothyroidism is a condition in which thyroid gland does not produce enough hormones. This condition may cause weight gain, dry skin, constipation, feeling cold and slow heart rate. Your doctor may ask you to undergo this test if you exhibit any of these signs or symptoms.

Why This Test is Done?

The doctor may ask to get this test done if the patient is suffering from symptoms like unexplained weight loss or weight gain, fatigue, weakness, difficulty in concentrating which are common symptoms of thyroid disorders. In some cases, this test is performed to find out the effectiveness of the treatment. If a patient is on the treatment of artificial thyroid hormones then the doctor prefers this test to evaluate and to check the thyroid hormone levels in the body. This helps the doctor to rule out the patient’s disease condition.

Precautions:

Drugs like amiodarone, thiourea, lithium, phenylbutazone, sulfonamides and birth control pills may change the levels of Total Thyroxine T4 in the blood. Drugs like carbimazole, methimazole may affect the levels of TSH in blood. Hence, all medications should be reported to the doctor before undergoing this test.

During pregnancy, T3, T4 levels may be abnormal and usually, it becomes stabilized after a period of time.

Pathology test parameters:

The Thyroid Profile Total test has the following components i.e:- Total Thyroxine T4, Total Triiodothyronine T3, and Thyroid Stimulating Hormone TSH.

If the test results are in normal range then the thyroid gland is functioning normally and no need for further medical intervention.

In the case of increased T3 and T4 levels in the blood than the normal range then it may be due to transient hyperthyroidism, Hashimoto's thyroiditis (an auto-immune disorder where the immune system of own body attacks the thyroid gland and decreases the production of hormones that are required for the body), Grave’s disease (an immune system disorder which results in the overproduction of thyroid hormones), subacute thyroiditis (acute inflammation of the thyroid gland), toxic adenoma (increased hormone production from single large nodule/lump in the thyroid gland), toxic multinodular goiter, thyroid cancer, increased production of thyroid stimulating hormone.

If the levels of T4 and T3 are less than the normal range then it may be due to hypothyroidism, previous treatment of hyperthyroidism, subacute thyroiditis (acute inflammation of the thyroid gland), neck radiotherapy before the test, iodine deficiency or excessive iodine, pituitary dysfunction, idiopathic myxedema (severe hypothyroidism), tissue resistance to thyroid hormone, starvation, or long-term illness, etc.

If TSH levels alone increased and T4, T3 levels are within the range then it may be due to mild hypothyroidism.

In case of reduced levels of TSH, it may indicate hyperthyroidism. If all the three TSH, T4 and T3 levels are low then it may be caused by nonthyroidal illness or pituitary hypothyroidism.