PATHOLOGY

MORE INFORMATION ABOUT THYROID BLOOD TESTS

• Thyroid stimulating hormone (TSH): This test is the initial indicator for thyroid disorders. TSH is produced by the anterior pituitary gland after stimulation from thyrotropin releasing hormone (TRH) secreted by the hypothalamus. TRH then triggers the pituitary gland to release TSH. The level of TSH rises when thyroid hormone levels (T4) in the blood decline. Conversely, the level of TSH declines as the thyroid hormone (T4) level in the blood rises.
• Thyroxine (T4): This test is used for a patient’s initial diagnosis and for monitoring thyroid replacement hormone levels (Levothyroxine) in the blood.
• Total T4 - Measures the total amount of thyroxine in the blood. This includes the amount attached to blood proteins that help transport the hormone through the bloodstream.
• Free T4 - Measures thyroxine that is not attached to proteins. This level of free hormone is what exerts the biological effect. This test shows how the hormone affects the functioning of many types of body cells.
• Triiodothyronine (Free T3): Measures the level of T3 in the blood. This test is useful for confirming an overactive thyroid (hyperthyroidism/Graves’ Disease). It also shows Levothyroxine absorption.
• Antithyroglobulin (anti-Tg) antibodies: This test is used to diagnose autoimmune thyroid disease. (Graves’/Hashimoto’s Diseases).
• Antithyroid peroxidise (anti-TPO) antibodies: This test is used to diagnose autoimmune thyroid disease, particularly Hashimoto’s Disease

Imaging of the thyroid gland and adjacent structures in the neck by nuclear medicine radioisotope scans, computerised tomography (CT) and Resonance Imaging (MRI) scans

• Your treating Doctor may request some form of imaging investigation to confirm or exclude abnormal function or structure of your thyroid gland. By far the commonest and most helpful form of imaging the thyroid and other soft tissues in the neck is by an Ultrasound examination.
• Radioisotope scans of the thyroid are Nuclear Medicine investigations used to investigate the functional ability of the thyroid by the uptake of radioisotope of iodine and to outline any increased or decreased activity of the whole thyroid gland or of individual and multiple thyroid nodules.
• These scans are frequently performed as a follow-up looking for any residual thyroid tissue after surgical removal of the thyroid for cancer and subsequent radiation treatment. A low dose of radioactive iodine – usually 13I in Australia- or Technetium Tc99m is administered orally so that the isotope uptake into the thyroid can be measured, and images of the thyroid gland can be obtained by special Nuclear Medicine instruments.
• A Nuclear Medicine Sestamibi Parathyroid scan is used to localise parathyroid tumours in the neck usually behind or adjacent to the thyroid gland. This is called a Sestamibi scan because the radioactive material Tc99m-sestamibi is used for imaging. Identification and localisation of the parathyroid tumour enables the surgeon to undertake minimal-access surgical removal of the parathyroid tumour.
• Computerized Tomography (CT) scans of the thyroid and adjacent structures in the neck may be required to determine the structure and position of an enlarged thyroid gland (goitre) and to determine if a goitre is pressing on and obstructing the windpipe (trachea) or any retrosternal extension into the chest cavity.
  For these CT scans, and generally most diagnostic CT scans for other purposes, a radiocontrast agent is usually administered intravenously prior to the CT scan. These radiocontrast agents enhance the quality of the CT images, but they contain large concentrations of iodine and can precipitate hyperthyroidism (overactivity of the thyroid gland) in patients with Graves’ disease or autonomously functioning nodular goitres. The need for administration of radiocontrast agents should be discussed with the doctor when the CT scan is ordered in patients who may be at risk of developing hyperthyroidism from the iodine in the contrast solution.
• Magnetic Resonance Imaging (MRI) scans use strong magnetic fields and radio waves to produce images of internal organs, as well as blood vessels, muscles, tendons, and other soft tissues in the body. There is no radiation or X-rays involved and contrast agents if used, do not contain iodine. MRI scans cannot be used in patients with metallic implants such as pacemakers. They are rarely used for imaging in patients with thyroid disorders except for patients with thyroid cancer which may have recurred or spread to other organs.
• Please Note: If you have been diagnosed with Graves’ Disease, Hyperthyroidism, a Nodular Goitre or Heart Disorder, please speak to your doctor about performing the CT scan or MRI Scan without Iodine Contrast Solution. The Iodine Contrast Solution can cause hyperthyroid symptoms which can be harmful. The CT scan or MRI Scan can be performed without the iodine contrast solution.
• Read Q&A about Iodine Contrast Solutions – Used in CT scans & Other X-Rays by Professor Jim Stockgit.
• All patients with hyperthyroidism and heart conditions need to be aware of issues relating to these solutions.
• Fine Needle Biopsy - Fine needle biopsy, also known as fine-needle aspiration cytology (FNAC), is usually done with the aid of ultrasound by a specialist doctor. A very fine needle is inserted into the thyroid gland to extract tissue from a nodule/s. This tissue is sent to a pathologist for testing. A FNB is used in the diagnosis of nodules and in particular identifying cells that may be cancerous.

Being aware is important, your thyroid health is essential to your wellbeing and general health, so speak to your doctor, if you have any symptoms or concerns.

If you have any questions or would like information, please email:  info@thyroidfoundation.org.au