To help diagnose hyperthyroidism and to monitor it's treatment
FT3
A blood sample taken from a vein in the arm
None needed; however, certain medications can interfere with the FT3 test, so tell your doctor about any drugs that you are taking
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How is it used?
A FT3 blood test determines whether the thyroid is performing properly, and is used mainly to help diagnose hyperthyroidism, since FT3 can become abnormally high earlier than FT4 and return to normal later than FT4.
FT3 is not usually helpful if your doctor thinks you have hypothyroidism.
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When is it requested?
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What does the test result mean?
A high free T3 result may indicate an overactive thyroid gland (hyperthyroidism).
A low free T3 results may indicate an underactive thyroid gland (hypothyroidism).
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Is there anything else I should know?
Many medications—including oestrogen, certain types of contraceptive birth control pills, and large doses of aspirin—can interfere with total T3 test results, so tell your doctor about any drugs you are taking. However, in general, free T3 concentrations are affected much less by these medications.
When you are sick, your body decreases production of T3 from T4. Most people who are sick enough to be in the hospital will have a low free T3 concentration in their blood. For this reason, doctors do not usually use FT3 as a routine thyroid test for patients in hospitals. -
How is hyperthyroidism treated?
Hyperthyroidism can be controlled through treatment. This will normally involve either tablets which stop the thyroid gland producing thyroid hormones, radioiodine treatment which destroys thyroid tissue, or surgery to remove part or all of the thyroid gland.
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How is hypothyroidism treated?
Hypothyroidism is easily treated and controlled for most people with thyroxine (T4) replacement in the form of a tablet.
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How does pregnancy affect thyroid hormone levels?
During pregnancy total T3 (and total T4) levels can increase. Normally, free T3 levels will not change significantly as a result of pregnancy. Even if total T3 levels rise during pregnancy, it does not mean thyroid disease will develop.