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Understanding your thyroid function results

Te mārama ki ō hua whakamātaunga oranga repe tenga

Illustration showing the thyroid gland, larynx (voice box) and trachea (windpipe)Your thyroid is a butterfly-shaped gland in your neck. It releases hormones into your bloodstream that control how your body functions. These hormones affect your temperature control and heart rate and turn the food you eat into energy. This is called your metabolism.

A thyroid function test (TFT) is used to check if your thyroid is underactive (hypothyroid) or overactive (hyperthyroid), or to see how well your thyroid treatment is working.

Terms used

TSH: this stands for thyroid stimulating hormone and is the most useful measurement to see how your thyroid is working. TSH is a hormone made by your pituitary gland (at the base of your brain). It controls your thyroid. This hormone goes into your bloodstream and stimulates your thyroid to release its hormones. If this test is normal, you probably will not have the following tests.

FT4: this is free thyroxine, the main hormone your thyroid makes.

FT3: this is free triiodothyronine, another hormone your thyroid makes.

Normal results

If you have a copy of your test results, it will show your results and a normal range for each test. The normal ranges may vary depending on your gender and age group and whether you're pregnant or have any underlying health conditions. So, the normal ranges shown on your test results may not be exactly right for you. Discuss your results with your general practice team if you're unsure.

High results

If your TSH is high and your FT4 is low, this shows that your thyroid is underactive (hypothyroidism).

If your TSH is high and your FT4 is normal, you may be at risk of having an underactive thyroid in the future. You may need repeat blood tests to monitor this every six to 12 months.

Low results

If your TSH is low and your FT4 and or FT3 are high, you have an overactive thyroid (hyperthyroidism).

If your TSH is low and your FT4 and or FT3 are normal, you should repeat the test in six to12 months.

Next steps

If your blood tests are too high or too low, you'll need to talk to your health provider about what treatment you need.

If you have an underactive thyroid, this is easily treated with thyroxine tablets that you take every day.

If you have an overactive thyroid, there are several ways of treating this, including medicines, radioiodine and surgery. Talk with your doctor about which is best for you.

If you're taking thyroxine tablets, the aim is for your TSH to stay in the normal range. This shows you're getting the right dose.

You can find more information in the thyroid section. Talk to your general practice team about your treatment options and any other questions you have.

Written by HealthInfo clinical advisers. Last reviewed October 2022.

Sources

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