Thyroid Function Blood Test
Is it for you?
If you are being treated for an underactive thyroid, yet still experience symptoms, this test can help explain your systems as it measures three thyroid hormones, including FT3, which your doctor may not routinely check. If you already take thyroid medication, like levothyroxine, you can find out if your dose is working well with this thyroid test.
- Thyroid Hormones
Thyroid Hormones (3 Biomarkers)
From the expert
Our Thyroid Function Blood Test is an excellent test to check and monitor your three key thyroid hormone levels – TSH, FT3 and FT4. The thyroid gland produces two of these hormones, T3 and T4, which are bound to proteins as they are transported around the body. When thyroid hormones are bound, they are not readily available to your cells. This test measures the level of free or unbound thyroid hormones, which are biologically active, as they are a better measure of your thyroid function than measuring total levels of T4 and T3 - and they are more likely to explain any symptoms that you may have.
Many routine tests that only include TSH and FT4 don't identify people who do not convert FT4 to the more biologically active FT3 easily. It is possible to have optimal levels of TSH and FT4 but still experience symptoms of an underactive thyroid if your levels of FT3 are low. This is particularly important if you are being treated for an underactive thyroid yet still experience symptoms. Measuring your FT3 is also important if you are taking some form of T3 medication like liothyronine or natural desiccated thyroid (NDT).
The third hormone, TSH, is produced by the pituitary gland in the brain. When functioning properly, it stimulates the thyroid gland to produce your thyroid hormones (mostly T4). We can think of this as a control hormone as it is responsible for controlling the levels of your thyroid hormones. High levels of TSH can signify that your thyroid is struggling to produce enough T4 for your body's needs. TSH on its own does not necessarily give a true picture of your thyroid function, which is why it is important to test the thyroid hormones too.
Have a look at our Thyroid Health Guide for how your thyroid could hold the answers to better skin, losing weight and regaining your energy.
Although anyone can develop a thyroid disorder, factors including being female or over the age of 50, and people with a family history of thyroid problems, can increase an individual’s risk of developing thyroid disease.
Thyroid results during pregnancy:
- Underactive thyroid during pregnancy – TSH level should be less than 2.5 mU/l in the first trimester and less than 3.0 mU/l in the second and third trimesters.
- Overactive thyroid during pregnancy - doses may be adjusted through regular monitoring.
Why take this test?
- Test your TSH, FT4 and FT3.
- Investigate symptoms of an underactive or overactive thyroid.
- See if your current thyroid medication dose is working.
- Take a more in-depth look at your thyroid than is routinely measured.
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