Thyroid Stimulating Hormone (TSH)

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.

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.  




Any preparation?


Reading your test report

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. It is usually followed by a free T4 and/or free T3 tests) to investigate the cause.  A ‘free’ T4 or T3 test refers to the fact that these hormones are circulating freely and available to be absorbed by body tissues.

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.  

High TSH result

  • A high TSH result may mean an underactive thyroid gland (hypothyroidism)
  • A high TSH result can also occur in people with underactive thyroid glands who have been receiving too little thyroid hormone medication
  • TSH can also be high when someone has an illness. If you are not well, it is important to check again when you have recovered.


Low TSH result

  • A low TSH result may indicate an overactive thyroid gland (hyperthyroidism) or a problem with your pituitary – depending on your thyroid hormone results. 
  • A low TSH result can also occur in people with an underactive thyroid gland who are receiving too much thyroid hormone medication.
  • Very rarely, a high TSH result can indicate a problem with the pituitary gland, such as a tumour, in what is known as secondary hyperthyroidism, or a genetic condition where the pituitary gland doesn’t respond to thyroid hormone levels as it should.


Patterns of thyroid function tests 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.


Reference intervals

Your results will be compared to a reference interval (sometimes called a normal range or reference range). 

  • Reference intervals are the range of results expected in healthy people 
  • When compared against them your results may be flagged high or low if they sit outside this range
  • Thyroid testing reference intervals may be different between different labs

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.

The choice of tests your doctor makes will be based on your medical history and symptoms.   It is important that you tell them everything 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?

Results for TSH may be low during the first trimester of pregnancy. This is because one of the hormones of pregnancy (HCG) has a TSH-like affect so the pituitary is not required to produce as much TSH.

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 from healthdirect.