What does TSH stand for?

TSH stands for Thyroid-Stimulating Hormone. It is produced by the pituitary gland and tells the thyroid how much hormone to make. TSH is the most sensitive first-line test for thyroid function.

TSH is tested to check for underactive thyroid (hypothyroidism), overactive thyroid (hyperthyroidism), to monitor people on thyroid medication, and to investigate fatigue, weight changes, mood disorders, fertility problems, or symptoms affecting the heart rate.

Do I need to fast before a TSH test?

No. Fasting is not required for a TSH test. However, some medications and supplements — including biotin — can interfere with results. Tell your doctor and the laboratory about anything you take.

What other tests are ordered with TSH?

If TSH is outside the reference range, your GP will usually order Free T4 (FT4) to measure the active thyroid hormone directly. Free T3 (FT3) and thyroid antibodies may also be ordered depending on the clinical picture.

What Is a TSH Test? — Thyroid Function Explained

What TSH measures

TSH stands for Thyroid-Stimulating Hormone. It is produced by the pituitary gland in the brain, not the thyroid itself. TSH tells the thyroid gland how hard to work — how much thyroid hormone (T4 and T3) to produce and release.

When thyroid hormone levels in the blood are low, the pituitary releases more TSH to stimulate the thyroid to produce more. When thyroid hormone levels are high, TSH falls to reduce stimulation. This feedback loop means TSH is an extremely sensitive indicator of thyroid function — small changes in thyroid hormone cause large changes in TSH.

TSH is the first-line test for assessing thyroid function. A normal TSH almost always indicates that thyroid hormone levels are within the healthy range.

Why your GP ordered it

TSH is ordered to assess thyroid function in a wide range of situations:

Symptoms that may suggest an underactive thyroid: fatigue, weight gain, feeling cold, constipation, dry skin, hair loss, low mood, slow heart rate
Symptoms that may suggest an overactive thyroid: weight loss, feeling hot, palpitations, anxiety, tremor, frequent bowel motions, insomnia
Monitoring people already on thyroid medication (thyroxine / levothyroxine)
Routine checks in pregnancy — thyroid disorders are common and important to manage in pregnancy
Investigating depression, anxiety, or cognitive changes — thyroid dysfunction can mimic or worsen these conditions
Fertility investigations

What the test involves

TSH is measured from a blood sample. No fasting is required. The result is usually available within 24 hours.

If your TSH is outside the reference range, your GP will usually order additional tests — Free T4 (FT4) and sometimes Free T3 (FT3) — to get a fuller picture of thyroid function.

📋 Source: Royal College of Pathologists of Australasia (RCPA) Pathology Manual — thyroid function tests. Endocrine Society of Australia. RACP thyroid guidelines. Reference range: TSH 0.5–4.0 mIU/L (adults, varies by lab and age). rcpa.edu.au
Your doctor or healthcare provider knows your history and circumstances — always follow their personalised advice over general information.

Some medications, supplements, and biotin (a common vitamin) can interfere with thyroid tests. Tell your GP and the laboratory about everything you take.

Australian laboratory context

In Australia, TSH is reported in mIU/L (milli-international units per litre). Reference ranges vary slightly between laboratories but are typically in the range of 0.4–4.0 mIU/L.

TSH reference ranges are calculated from population data and represent the middle 95% of healthy adults. This means 5% of healthy people fall outside the range — so a result slightly outside the range does not automatically indicate disease.

TSH varies slightly at different times of day and across the menstrual cycle. Repeat testing is often used to confirm an abnormal result before treatment decisions are made.

Your GP will interpret your results in the context of your full medical history, your symptoms, your medications, and any previous results. A result outside the reference range does not automatically mean something is wrong, and a result within range does not always mean there is no problem. Always discuss your results with your GP or the clinician who ordered the test.