Te mārama ki ō hua whakamātaunga oranga repe tenga Understanding your thyroid function results
Your thyroid is a gland in your neck. It releases hormones that help control body functions, including your temperature, heart rate and metabolism. A thyroid function test (TFT) is a blood test that can check if your thyroid is underactive (hypothyroid) or overactive (hyperthyroid). If you have thyroid disease, the test will be used monitor your treatment.
Terms used in your thyroid function results
Thyroid stimulating hormone (TSH)
TSH stands for thyroid stimulating hormone. TSH 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 will probably not need the FT4 and FT3 tests.
Free thyroxine (FT4)
FT4 is free thyroxine, the main hormone your thyroid makes.
Free triiodothyronine (FT3)
FT3 is free triiodothyronine, another hormone your thyroid makes.
Normal thyroid function 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
- your age group
- whether you are pregnant
- any underlying health conditions.
So the normal ranges shown on your test results may not be exactly right for you. Talk to your healthcare provider about your results if you are unsure.
High TSH results
If your TSH result is high and your FT4 result is low, this shows your thyroid is underactive (hypothyroidism).
If your TSH result is high and your FT4 result 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 6 to 12 months.
Underactive thyroid (hypothyroidism) — Healthinfo (external link)
Low TSH results
If your TSH result is low and your result for FT4, FT3, or both are high, you have an overactive thyroid (hyperthyroidism).
If your TSH result is low and your FT4, FT3, or both are normal or low, another illness not related to your thyroid gland may be the cause. You may need further tests.
Overactive thyroid (hyperthyroidism) — Healthinfo (external link)
Next steps
If your thyroid function blood test results are too high or too low, you will need to talk to your healthcare provider about what treatment you need.
If you are on treatment for your thyroid, your healthcare provider will tell you if any changes are needed.