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Summary

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.

  • The pituitary gland at the base of your brain controls your thyroid.
  • It produces Thyroid Stimulating Hormone (TSH) that interacts with the thyroid gland to increase or decrease production of T4 and T3 when levels are too low or too high.
  • If thyroid hormone levels are too low, TSH rises and conversely if thyroid hormones become too high, TSH levels fall.

 

Thyroid function tests 

If you have symptoms that suggest you have a thyroid problem your doctor will start by ordering:

  • A Thyroid Stimulating Hormone (TSH) test which is used to test for hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid), to screen newborn babies for hypothyroidism, and to monitor treatment with thyroid hormone tablets.  

If the results of this are too high or low, a free T4 and/or free T3 test will be ordered.

  • FT4 – to test for hypothyroidism and hyperthyroidism.
  • FT3 – to test for hyperthyroidism.

Often the laboratory performing your testing will automatically go on to perform a free T4 test or free T3 test on your original blood sample.  

 

 

Autoimmune conditions

Autoimmune conditions occur when your immune system, designed to defend you, mistakenly makes antibodies that attack healthy tissue.

Thyroid antibodies – also called autoantibodies – are antibodies that a person’s immune system makes that mistakenly targets the thyroid gland or thyroid proteins.  This leads to chronic inflammationjust for test of the thyroid, tissue damage, and/or disruption of thyroid function.

There are two main autoimmune conditions that affect the thyroid gland:

  • Hashimoto's thyroiditis  – the immune system attacks the thyroid gland, causing inflammation which slows the production of thyroid hormones. Having not enough thyroid hormone results in an underactive thyroid (hypothyroidism).
  • Graves’ disease – the immune system makes an antibody that acts like Thyroid Stimulating Hormone (TSH) and causes the thyroid gland to produce too much thyroid hormone.  Having too much thyroid hormone results in an overactive thyroid (hyperthyroidism).

 

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.

Some of the antibody tests used are:

  • Thyroid peroxidase antibodies (TPO) 
  • Thyroid-stimulating hormone (TSH) receptor 
  • Thyroid-stimulating immunoglobulin (TSI)

Often the laboratory performing your testing will automatically go on to perform a free T4 test or free T3 test on your original blood sample.  

A ‘free’ T4 or T3 test refers to the fact that the type of hormone being tested is the part which is circulating freely and available to be absorbed by body tissues.

 

Thyroid antibody

Present in

When ordered

Other facts

Thyroid peroxidase antibody (TPO Ab)

Hashimoto's thyroiditis & Graves' disease

When someone has symptoms suggesting thyroid disorder;

when a doctor is considering starting a patient on a drug therapy that may cause thyroid

dysfunction when these antibodies are present (eg, lithium, amiodarone, interferon alpha 

or interleukin - 2).

Has been associated with reproductive difficulties, such as 

miscarriage, pre-eclampsia, premature deliver, and in-vitro fertilisation failure.

Thyroglobin antibody (TG Ab)

Hashimoto's thyroiditis; in some patients being monitored for thyroid cancer

Whenever a thyroglobulin test is performed to see if the antibody is present and likely to be interfering with the test results; at regular intervals after thyroid cancer treatment; when symptoms of hypothyroidism are present.

Not sensitive as TPO antibodies in diagnosing autoimmune thyroid disorder.


 

 

Having the test

Sample

Blood


Any preparation?

None

Your results

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.  

In general, the presence of thyroid antibodies suggests that there is autoimmune thyroid involvement and the higher the level of antibodies in the blood sample, the more likely this is the case. 

Rising levels may be more significant than stable levels as they indicate an increase in autoimmune activity. All of these antibodies, if present in a pregnant woman, can increase the risk of hypothyroidism or hyperthyroidism in the developing baby or newborn.

A certain percentage of people who are healthy may be positive for one or more thyroid antibodies. The prevalence tends to be higher in women and tends to increase with age. If a person with no apparent thyroid dysfunction has a measurable thyroid antibody, their doctor will track their health over time. While most of these people may never experience thyroid dysfunction, a few may develop it in the future.

 

Thyroid antibody tests – what results may indicate

Test results

Indication

 

No thyroid antibodies detected 

Autoantibodies are not present in the blood at the time of testing and may indicate that symptoms are due to a cause other than autoimmune thyroid disorder. However, a small group of people with autoimmune thyroid disorder do not have detectable thyroid autoantibodies.

Mild to moderately high levels of thyroid antibodies

Could be a variety of thyroid and autoimmune disordersType 1 diabetesrheumatoid arthritispernicious anaemia, and autoimmune collagen vascular disorders, as well as thyroid cancer. 

Significantly high concentrations

Usually indicates a thyroid autoimmune disorder such as Hashimoto’s thyroiditis or Graves’ disease.

Table 2. 

 

 

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:

  • Why does this test need to be done?
  • Do I need to prepare (such as fast or avoid medications) for the sample collection?
  • Will an abnormal result mean I need further tests?
  • How could it change the course of my care?
  • What will happen next, after the test?

Any more to know?

If TGAb are present when monitoring thyroglobulin levels in someone who has been treated for thyroid cancer, the antibodies may interfere with the thyroglobulin test result. This may mean that the doctor will not be able to use thyroglobulin as a tumour marker for thyroid cancer. 

Thyroglobulin results must be interpreted with extreme caution in people with anti-TG antibodies, and it is likely that another test such as a thyroid ultrasound will be required to assess for any evidence of cancer recurrence.
 

More information

Related tests on PTEX:

 
TSHFree thyroxine (FT4 ; Free triiodothyronine (FT3); thyroid antibodiesthyroglobulincalcitonin

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed. Get further trustworthy health information and advice fromhealthdirect.


 

Last Updated: Thursday, 1st June 2023

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