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Understanding your thyroid function results
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 is used to check if
your thyroid is underactive (hypothyroid) or
overactive (hyperthyroid), or to see how
well your thyroid treatment is working.
What is a normal result?
A normal result will be within the following ranges:

TSH between 0.4 and 4 mIU/L

FT4 55 to 160 nmol/L (this isn't always tested)

FT3 2.5 to 6 pmol/L (this isn't always tested).
What do the different terms mean?
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 then you probably won't have the following tests.
FT4: this is free thyroxine, the main hormone your thyroid makes.
FT3: this is free tri-iodothyronine, another hormone your thyroid makes.
What does it mean if my results are too high?
If your TSH is high and your FT4 is low this shows that your thyroid is underactive (hypothyroidism).
If you 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.
What does it mean if my results are too low?
If your TSH is low and your FT4 and or FT3 are high, then you have an overactive thyroid
(hyperthyroidism).
If your TSH is low and your FT4 and or FT3 are normal, then you should repeat the test in six to12 months.
HealthInfo reference: 269156
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Issued: 21 June 2016
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Page 1 of 2
Understanding your thyroid function results
www.healthinfo.org.nz
What happens next?
If your blood tests are too high or too low, you will 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, or surgery. Talk with your doctor about which is best for you.
If you are taking thyroxine tablets, the aim is for your TSH to stay in the normal range. This shows you
are getting the right dose.
You can find more information in the thyroid section of HealthInfo. Talk to your doctor about your
treatment options and any other questions you have.
Written by HealthInfo clinical advisers. June 2016.
269156
HealthInfo reference: 269156

Issued: 21 June 2016

Page 2 of 2