Thyroid Function Tests (TFT)

Muktadir HosenExecutive- PMDLabaid Group

Thyroid Function TestBlood tests that check the levels of the hormones (chemicals) made by the thyroid gland. Some thyroid function tests also check the level of a hormone made by the pituitary gland in the brain, which acts on the thyroid gland.

Thyroxine (T4) Triiodotyronine (T3) Thyroid stimulating hormone (TSH) Free T4 Free T3

Thyroid Hormones

The Iodine is the most important element in the biosynthesis of thyroid hormones.

Thyroglobulin acts as a performed matrix containing tyrosyl groups to which the reactive iodine attaches to form the hydroxyl residues of monoiodotyrosine (MIT) & diiodotyrosine (DIT).

The coupling of two DIT molecules forms T4. The coupling of one DIT molecules & one MIT

molecule results in the formation of T3 or reverse T3 (rT3).

Almost all circulating T4 & T3 hormones are bound to serum proteins (thyroid hormone-binding proteins).

Formation of T3

Formation of T4

Only 0.03 % of T4 & 0.3 % of T3 are not bound to proteins.

These fractions, called free T4 (FT4) & free T3 (FT3), are the physiologically active portions of the thyroid hormones.

Free T3 & Free T4

Two types of Thyroid Diseases1. Hypothyroidism (underactive

thyroid)2. Hyperthyroidism (overactive

thyroid)

How do thyroid function tests work?

In Hypothyroidism - Thyroid is not making enough T3 to stop the pituitary producing TSH. If the level of TSH is high, you will usually have further tests to check the levels of T3 and T4 in the blood.In Hyperthyroidism - The level of TSH will usually be low. because the thyroid gland is making too much of its hormones. When levels of T3 and T4 are high, the pituitary is 'turned off' and the amount of TSH produced is less. If you are found to have low levels of TSH you may have some more blood tests to check the levels of T3 and T4 in the blood. These tests may help doctors to find a specific cause of the low TSH.

Symptoms of Hypo and HyperThyroidism

Causes of Hypothyroidism

Hashimoto’s thyroiditis – Thyroiditis is an inflamation of the thyroid gland. Hashimoto’s thyroiditis is an autoimmune disorder. With Hashimoto’s, body produces antibodies that attack and destroy the thyroid gland. Thyroiditis may also be caused by a viral infection.

Radiation therapy to the neck area.

Dose of certain medication. Thyroid surgery. Low amount of iodine in diet.

Graves disease – it causes the thyroid gland to make too much thyroid hormone.

Thyroid nodules – abnormal growth of thyroid gland that can make to much thyroid hormone.

Thyroiditis – occurs when body makes antibodies that damage thyroid gland. It can also occur for viral or bacterial infection. At first, thyroiditis may cause your thyroid levels to rise as hormone leaks out from the damaged gland. Later, levels may be low (hypothyroidism) until the gland repairs itself.

High amount of Iodine in diet.

Causes of Hyperthyroidism

Regulation of carbohydrate, lipid & protein metabolism.

Central nervous system activity & brain development

Cardiovascular stimulation Bone & tissue growth & development Gastrointestinal regulation

Functions of thyroid hormones

What are thyroid function tests used for?Find out whether the thyroid gland is working properly. This is mainly to diagnose underactive thyroid (hypothyroidism) and overactive thyroid (hyperthyroidism). Thyroid function tests can also be done to: Monitor treatment with thyroid replacement medicine for people who have hypothyroidism.

Check thyroid gland function in people who are being treated for hyperthyroidism.

Screen newborn babies for inherited problems with the thyroid.

The tests used to investigate thyroid function can be grouped into:

Tests that establish whether there is thyroid dysfunction:

TSH, total T4 & total T3 measurements.

Thyroid functions tests

What happens during a thyroid function test?

Simple blood test. Blood sample is then sent to the laboratory for analysis, and the results are sent back to the doctor who asked for the tests.

Preparation need for the test

Require very little preparation.

Need to inform doctor about medication because some drugs may alter the test result

Also important to mention any X-ray tests that have used a special contrast dye as this may contain iodine which can affect the results.

Levels of thyroid hormones also change in pregnancy, so tell your doctor if you are pregnant when the test is taken.

Labaid Thyroid test listSerum F - T3 Serum F - T4 Serum T3Serum T4Serum TSHSerum T4,T3,THSAnti-Thyroglobulin AbAnti-Thyroid AntibodyAnti Thyroid Peroxidase Antibody

Thyroid Peroxidase Thyroid peroxidase (TPO) is an enzyme made in the

thyroid gland that is important in the production of thyroid hormone.

Thyroid peroxidase test is a test that measures the level of an antibody that is directed against thyroid peroxidase (TPO).

Autoantibodies to thyroid peroxidase (TPOAb) are produced within the body. The presence of TPOAb in the blood reflects a prior attack on the thyroid tissue by the body's immune system.

Anti-Thyroglobulin Ab Antithyroglobulin antibodies can be a sign of

thyroid gland damage caused by the immune system. Such antibodies are more likely to appear after thyroid gland swelling (inflammation) or injury.

Thyroglobulin antibody is also measured to monitor patients who have had their thyroid gland removed because of thyroid cancer.

A negative test is normal. It means no antibodies to thyroglobulin are found in your blood.

A positive test means antithyroglobulin antibodies are found in your blood

Thyroid Antibody

Thyroid antibody testing is primarily ordered to help diagnose an autoimmune thyroid disease and to distinguish it from other forms of thyroid dysfunction.

It may be ordered to help investigate the cause of a goiter or other signs and symptoms associated with low or high thyroid hormone levels.

Testing may be performed as a follow-up when other thyroid test results (such as T3, T4, and/or TSH) indicate thyroid dysfunction.

Thyroid hormones are analyzed by: ELISA RIA Chemiluminescence Fluorescent immunoassay

Analysis of thyroid hormones

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