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THYROID FUNCTION TEST Presented by: Dr. P. Pasupathi, Ph.D.,FLS (UK).,


INTRODUCTION THYROID HORMONES : DEFINITION The thyroid gland is a butterfly-shaped that is normally located in the lower front of the neck. The gland produces thyroid hormones, which regulate body metabolism. Thyroid hormones are important in regulating body energy, the body's use of other hormones and vitamins, and the growth and maturation of body tissues.

The major thyroid hormones : 

The major thyroid hormones Thyroid-Stimulating Hormone (TSH) Thyroxine (T4) and Triiodothyronine (T3) ,(Free T3 and Free T4) A thyroid-stimulating hormone (TSH) blood test is used to check for thyroid gland problems. TSH is produced when the hypothalamus releases a substance called thyrotropin-releasing hormone (TRH). TRH then triggers the pituitary gland to release TSH.

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Triiodothyronine (T3) and thyroxine (T4) are needed for normal growth of the brain, especially during the first 3 years of life. A baby whose thyroid gland does not make enough thyroid hormone (congenital hypothyroidism) may, in severe cases, be mentally retarded. Older children also need thyroid hormones to grow and develop normally. Diseases of the thyroid gland : Hhyperthyroidism Hhypothyroidism

Hyperthyroidism : : 

Hyperthyroidism : Hyperthyroidism :Thyroid gland makes too much thyroid hormone. Excess thyroid hormone can cause symptoms such as:        tiredness,        weight loss,        increased heart rate,        heat intolerance,        sweating,        irritability,        anxiety, muscle weakness, and thyroid enlargement

Hypothyroidism : : 

Hypothyroidism : Hypothyroidism : Thyroid gland does not produce enough thyroid hormone, which regulates the way the body uses energy.   An underactive thyroid gland (hypothyroidism) can cause symptoms such as:         weight gain,         tiredness,         dry skin, constipation,         brittle nails, or a yellowish tint to the skin.         a feeling of being too cold, or frequent menstrual periods.


THYROID GLAND FUNCTION ·        The major thyroid hormone secreted by the thyroid gland is thyroxine, also called T4 because it contains four iodine atoms.         To exert its effects, T4 is converted to triiodothyronine (T3) by the removal of an iodine atom. This occurs mainly in the liver and in certain tissues where T3 acts, such as in the brain.         The amount of T4 produced by the thyroid gland is controlled by another hormone, which is made in the pituitary gland located at the base of the brain, called thyroid stimulating hormone(TSH).

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The amount of TSH that the pituitary sends into the blood stream depends on the amount of T4 that the pituitary sees. If the pituitary sees very little T4, then it produces more TSH to tell the thyroid gland to produce more T4.         Once the T4 in the blood stream goes above a certain level, the pituitary’s production of TSH is shut off. In fact, the thyroid and pituitary act in many ways like a heater and a thermostat. When the heater is off and it becomes cold, the thermostat reads the temperature and turns on the heater.         When the heat rises to an appropriate level, the thermostat senses this and turns off the heater. Thus, the thyroid and the pituitary, like a heater and thermostat, turn on and off.

THYROID GLAND FUNCTION This is illustrated in the following figure: : 

THYROID GLAND FUNCTION This is illustrated in the following figure:

Tests to evaluate thyroid function: : 

Tests to evaluate thyroid function: Blood tests to measure TSH, T4 and T3 (Free T3 and Free T4) are readily available and widely used. TSH Tests:   ·        The initially thyroid-stimulating hormone (TSH) blood test is used to check for thyroid gland problems. ·        A high TSH level indicates that the thyroid gland is failing because of a problem that is directly affecting the thyroid (primary hypothyroidism).   ·        The TSH level is low, usually indicates that the person has an overactive thyroid that is producing too much thyroid hormone (hyperthyroidism).

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Occasionally, a low TSH may result from an abnormality in the pituitary gland, which prevents it from making enough TSH to stimulate the thyroid (secondary hypothyroidism).         In most healthy individuals, a normal TSH value means that the thyroid is functioning normal. T4 Tests: T4 circulates in the blood in two forms:     T4 bound to proteins that prevent the T4 from entering the various tissues that need thyroid hormone and      Free T4, which does enter the various target tissues to exert its effects.

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Free- T4: The FT4 measures the concentration of free thyroxine, the only biologically active fraction, in the serum. The free thyroxine is not affected by changes in concentrations of binding proteins such as TBG and thyroid binding prealbumin. Thus such conditions as pregnancy, or estrogen and androgen therapy do not affect the FT4.

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The free T4 fraction is the most important to determine how the thyroid is functioning, and tests to measure this are called the Free T4 (FT4) and the Free T4 Index (FT4I or FTI).         Hyperthyroidism will have an elevated FT4 or FTI, Hypothyroidism will have a low level of FT4 or FTI.

TSH test with the FT4 or FTI accurately determines how the thyroid gland is functioning. : 

TSH test with the FT4 or FTI accurately determines how the thyroid gland is functioning.

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Combining the TSH test with the FT4 or FTI accurately determines how the thyroid gland is functioning.         The finding of an elevated TSH and low FT4 or FTI indicates primary hypothyroidism due to disease in the thyroid gland. A low TSH and low FT4 or FTI indicates hypothyroidism due to a problem involving the pituitary gland.         A low TSH with an elevated FT4 or FTI is found in individuals who have hyperthyroidism.

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T3 Tests:         T3 tests are useful to diagnosis hyperthyroidism or to determine the severity of the hyperthyroidism.         Patients who are hyperthyroid will have an elevated T3 level. What are the Difference Between T3 and Free T3? T3 is a thyroid hormone that circulates in blood almost completely bound (99.5%) to carrier proteins.

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The main transport protein is thyroxine-binding globulin (TBG). However, only the free (unbound) portion of triiodothyronine (free T3) is believed to be responsible for the biological action. Furthermore, the concentrations of the carrier proteins are altered in many clinical conditions, such as pregnancy. Measurements of Free T3 concentrations, therefore, correlate more reliably with your clinical status than Total T3 levels.

Interpretation : 

Interpretation Thyroid-Stimulating Hormone (TSH) This test is used to identify primary hypothyroidism and to differentiate it from secondary (pituitary) and tertiary (hypothalamus) hypothyroidism. Thyroxine(T4) This test is used to evaluate thyroid function. T4 is decreased in hypothyroidism and in the third stage of sub acute thyroiditis. T4 is increased with hyperthyroidism, sub acute thyroiditis in its first stage and with thyrotoxicosis due to Hashimoto disease.

The following table summarizes test results and their potential meaning. : 

The following table summarizes test results and their potential meaning.

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T4 is also used to diagnose toxicosis. Tri-iodothyronine (T3), Free, This test is used to evaluate thyroid function. It is primarily used to diagnose hyperthyroidism. It is also used to assess abnormal binding protein disorders Monitor thyroid replacement and suppressive therapy

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Thyroid testing is used to: Diagnose a thyroid disorder in a person with symptoms, Screen newborns for an under active thyroid, Monitor thyroid replacement therapy in people with hypothyroidism Diagnose and monitor female infertility problems, Help evaluate the function of the pituitary gland (occasionally), and Screen adults for thyroid disorders as recommended by some organizations, such as the American Thyroid Association.

Thyroid Problems Causes: : 

Thyroid Problems Causes: Hyperthyroidism Causes: An autoimmune disorder called Graves' disease is the most common cause of hyperthyroidism. Other causes include growths in the thyroid gland (thyroid nodules), inflammation of the thyroid gland (thyroiditis). And taking too much thyroid replacement hormone to treat an underactive thyroid (hypothyroidism).

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Hyperthyroidism can be treated with Medication, Radioactive iodine, or with surgery. In most cases, treatment brings thyroid function back to normal. However, lifelong follow-up with a health professional is needed to closely monitor thyroid hormone levels.

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Hypothyroidism Causes : Loss of tissue: Treatment of hyperthyroidism by radioactive destruction of thyroid tissue or surgical removal of thyroid tissue can result in hypothyroidism. Antithyroid antibodies: These may be present in people who have diabetes, lupus, rheumatoid arthritis, chronic hepatitis, These antibodies may cause decreased production of thyroid hormones. Congenital: Hypothyroidism can be present from birth. This is commonly discovered early with nationwide newborn screening for this disease.

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Defects in the production of thyroid hormone: Hashimoto thyroiditis occurs when there are defects in the production of thyroid hormone, resulting in an increased amount of TSH. The increased TSH results in a goiter (enlargement of the thyroid gland itself that can be seen as an obvious swelling in the front of the neck). Medications: Some medications, particularly lithium, may cause a drug-induced hypothyroidism

When to Seek Medical Care: : 

When to Seek Medical Care: The signs and symptoms of hypothyroidism and hyperthyroidism typically develop slowly over a period of weeks to months. If you have prolonged symptoms or signs of either condition, call your doctor to be evaluated. Untreated hypothyroidism may have severe effects on the brain as well as cause intestinal obstruction and inability of the heart to beat effectively.

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Seek immediate attention at a hospital’s emergency department if you have these signs and symptoms associated with thyroid problems. . Chest pain Shortness of breath Abdominal pain Vomiting Extreme agitation or irritability Coma

Exams and Tests: : 

Exams and Tests: The medical history and physical exam are important parts of the evaluation for thyroid problems. The doctor will focus on eye, skin, cardiac, and neurologic findings. Blood tests: Thyroid-stimulating hormone (TSH): In most cases, this is the single most useful lab test in diagnosing thyroid disease. When there is an excess of thyroid hormone in the blood, as in hyperthyroidism, the TSH is low.

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When there is too little thyroid hormone, as in hypothyroidism, the TSH is high. Thyroxine (T4): T4 is one of the thyroid hormones. High T4 may indicate hyperthyroidism. Low T4 may indicate hypothyroidism. Triiodothyronine (T3): T3 is another one of the thyroid hormones. High T3 may indicate hyperthyroidism. Low T3 may indicate hypothyroidism.

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THYROID ANTIBODIES Antithyroid antibody: This antibody is present in Hashimoto disease. Thyroid peroxidase antibody(or) Anti microsomal antibody(TPOAb). This antibody is present in Hashimoto disease; Graves' disease. Thyroglobulin antibody(TgAb). Present in Thyroid cancer; Hashimoto’s thyroiditis. TSH receptor antibody: This antibody is present in Graves disease.

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Thyroid scan: For this test, a small amount of radioactive iodine is given into the blood, and then an x-ray image of the thyroid is taken. Increased uptake of the radioactive material in the thyroid gland indicates hyperthyroidism, while decreased uptake is present in hypothyroidism. This test should not be done on pregnant women.

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Thyroid ultrasound: This exam helps to differentiate between different types of nodules of the thyroid gland. Fine-needle aspiration: For this test, a small needle is inserted into the thyroid gland in order to get a sample of thyroid tissue, usually from a nodule. The tissue is then observed under a microscope to look for any signs of cancer.

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TFT-NORMAL RANGE: (ABBOTT AXSYM –Immunoassay Analyzer)


LABORATORY: Fully automated instrument used for Thyroid Function Tests:   Instrument Name: ABBOTT AXSYM –Immunoassay Analyzer:        Clinical decisions demand the highest accuracy and precision available, and that's why over 10,000 laboratories worldwide have made AxSYM their choice for immunoassay assay testing.     The AXSYM processes up to 80 to 120 tests per hour while providing continuous access, random access, and STAT processing with a broad testing menu..

LABORATORY:Fully automated instrument used for Thyroid Function Tests: ABBOTT AXSYM –Immunoassay Analyzer: : 

LABORATORY:Fully automated instrument used for Thyroid Function Tests: ABBOTT AXSYM –Immunoassay Analyzer:

Quality system: : 

Quality system: Internal Quality Control(IQC): Primary control using Axsym Abbott –Instrument control.   Secondary control Using- BIO-RAD Internal quality Control. External Quality Control (EQAS): BIO-RAD(EQAS) LABORATORIES- Monthly Clinical Chemistry Report .

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