Thyroid conditions are common and can affect people of all ages from babies to the elderly. They can be caused by a range of underlying conditions. Your doctor will usually start by requesting a TSH test. This measures the amount of Thyroid Stimulating Hormone (TSH) in your blood. TSH is the hormone that stimulates your thyroid gland to make thyroid hormone. This is the only thyroid test covered by Medicare if you do not have a history of thyroid problems. Depending on your symptoms and your TSH result, you may need further testing of your thyroid hormones with measurement of FreeT4 and Free T3. If your doctor thinks you could have an autoimmune condition that is affecting your thyroid gland you may go on to have thyroid antibody tests. There are also tests that are used to monitor thyroid cancer following treatment. They include thyroglobulin and calcitonin tests which are used to detect and monitor some rare forms of thyroid cancer.
Why get tested?
Your thyroid is a small gland at the base of your throat. It uses iodine from your diet to make hormones that regulate many of your body’s metabolic processes – your body’s processes for breaking down food and converting it into energy. How your thyroid is working affects how fast you burn calories, your heart rate, blood pressure and body temperature..
There are two main hormones produced by the thyroid. These are T4 and T3. They circulate in your blood, and it is important that levels stay constant to keep your metabolism running and in balance.
There is a feedback mechanism to make sure they don’t get too high or too low.
Underactive and overactive thyroid conditions
Because the thyroid is important to so many bodily processes, too much or too little thyroid hormone can make you feel very unwell. Your doctor will be looking for:
Having the test
Reading your test report
Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.
Patterns of thyroid function test results and their most common causes.
Normal thyroid function
Mild (sub-clinical) underactive thyroid (hypothyroidism) or acute illness
Low or normal
Underactive thyroid - too little thyroid hormone being produced resulting from a problem with the thyroid (hypothyroidism)
Mild (sub-clinical) overactive thyroid (hyperthyroidism).
High or normal
High or normal
Overactive thyroid - too much thyroid hormone being produced (hyperthyroidism)
Hypothyroidism resulting from a problem with pituitary or hypothalamus signalling that control the thyroid gland.
Is it your pituitary?
No single pathology test can accurately diagnose all types of thyroid conditions. A combination of tests is usually needed to detect disorders of thyroid function and to differentiate between thyroid and pituitary gland problems.
For example, a low T4 level could mean that your thyroid isn’t producing enough T4 or that your pituitary gland is not stimulating the thyroid to produce T4. Since the pituitary gland would normally release TSH if the T4 is low, a high TSH level would confirm that it is your thyroid gland and not your pituitary gland that’s the problem.
If the T4 level and TSH are both low or if they are both high, the pituitary gland is more likely to be the cause. If this is the case, it would change the course of the investigation. The pituitary gland is involved in managing many of you hormones including your normal steroid, reproductive and growth hormones.
Tests for autoimmune conditions
Further tests may need to be performed if your doctor suspects that you have an underlying autoimmune condition – you have an enlarged thyroid or symptoms suggesting thyroid dysfunction. In this case you may need to have antibody tests.
Autoimmune conditions are when your immune system, designed to defend you, mistakenly makes antibodies that attack healthy tissue. There are two main autoimmune conditions affecting the thyroid:
Some of the antibody tests used are:
Tests for cancer diagnosis and monitoring
The thyroglobulin test is used as a tumour marker to assess the effectiveness of thyroid cancer treatment and to monitor for recurrence after the thyroid has been completely removed. Since thyroglobulin normally is made only in the thyroid, it should drop to very low or undetectable levels in these patients.
A calcitonin test is sometimes ordered to diagnose and monitor two rare conditions, C-cell hyperplasia and medullary thyroid cancer (MTC). In these conditions, large amounts of calcitonin are produced. C-cell hyperplasia is a benign condition that may or may not progress to become MTC. MTC is malignant which means it can spread beyond the thyroid and can be difficult to treat if it is not discovered early.
Your results will be compared to a reference interval (sometimes called a normal range or reference range).
If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor.
Questions to ask your doctor
The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell themeverything you think might help.
You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.
Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:
Any more to know?
Many multivitamins, supplements – especially biotin found in hair and nail supplements– and over-the-counter and prescription medications can affect thyroid test results, so tell your doctor about any drugs you are taking. Your thyroid hormone medication also affects results. When your doctor adjusts your dose of thyroid hormone, it is important that you wait at least one to two months before checking your TSH again, so that your new dose can have its full effect.
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