FT4 can tell whether the thyroid is performing properly. It aids in the diagnosis of hypothyroidism or hyperthyroidism. The test may also be used to help evaluate a patient with an enlarged thyroid gland, called a goitre. It may also aid in the diagnosis of female infertility problems.
Many medicines including oestrogen, certain types of contraceptive birth control pills, those drugs used to help control epilepsy and large doses of aspirin can interfere with total T4 test results, so tell your doctor about any drugs you are taking. In general, free T4 levels are not affected by these medications.
In addition, total T4 levels may be affected by contrast material used for certain X-ray imaging tests. Total T4 is now rarely measured in the UK having been replaced by Free T4 (FT4).
This article was last reviewed on 7 June 2011. | This article was last modified on 28 August 2013.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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