A free or total triiodothyronine (free T3
or total T3) test is used to assess thyroid function. It is ordered primarily
to help diagnose hyperthyroidism and may be ordered to help monitor treatment
of a person with a known thyroid disorder.
A free T3 or total T3 test may be ordered
when someone has an abnormal TSH test result. It may be ordered as part of the
investigative workup when a person has symptoms suggesting hyperthyroidism,
especially if the free T4 level is not elevated.
Signs and symptoms may include:
Increased heart rate
Anxiety
Weight loss
Difficulty sleeping
Tremors in the hands
Weakness
Diarrhea (sometimes)
Light sensitivity, visual disturbances
The eyes may be affected: puffiness around the eyes, dryness,
irritation, and, in some cases, bulging of the eyes.
Free or total T3 may sometimes be ordered
at intervals to monitor a known thyroid condition and to help monitor the
effectiveness of treatment for hyperthyroidism.
Results
Interpretations
Total T3 or free T3 results are typically
evaluated with other thyroid testing results (i.e., TSH and T4).
In general, high total or free T3 results
may indicate an overactive thyroid gland (hyperthyroidism) and low total or
free T3 results may indicate an underactive thyroid gland (hypothyroidism). The
test results alone are not diagnostic but will prompt the healthcare
practitioner to perform additional testing to investigate the cause of the
excess or deficiency.
When used for monitoring treatment for
thyroid or pituitary disorders, results of thyroid tests will inform the
healthcare practitioner whether treatment is effective and/or whether an
adjustment to dose is necessary. For example, in people with hyperthyroidism,
free T4, free T3, and TSH are regularly checked while they are on anti-thyroid
drugs to assure that the drugs are working and to decrease doses if thyroid
hormone levels get too low. In people with hypothyroidism, TSH and free T4 are
regularly checked to assure that the right dose of thyroid hormone is being
given to make TSH normal.
The following table summarizes some examples of typical test results and their potential meaning.
Keyword: T3 test; free and total T3; free and
total triiodothyronine.
* The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
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