FT4 is a direct measure of the free T4 hormone concentration (biologically available hormone).
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Increased in
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Decreased in
|
Hyperthyroidism, nonthyroidal
illness, especially psychiatric.
Drugs: amiodarone, β-blockers (high-dose). |
Hypothyroidism, nonthyroidal
illness.
Drugs: phenytoin. |
The free thyroxine is used along with sensitive TSH assays for detecting clinical hyperthyroidism
and hypothyroidism. The TSH assay detects subclinical thyroid dysfunction (normal FT4) and monitors
levothyroxine treatment better, whereas the free thyroxine test detects central hypothyroidism and
monitors rapidly changing function status better.
i. Elevated Free T3 and Free T4 with Low TSH: This often indicates
hyperthyroidism, where the thyroid gland is overactive.
ii. Low Free T3 and Free T4 with Elevated TSH: This usually points to
hypothyroidism, where the thyroid gland is underactive.
iii. Normal Free T3 and Free T4 with Normal TSH: This suggests that the thyroid is
functioning normally.
iv. Normal Free T3 and Free T4 with High TSH: This could indicate subclinical
hypothyroidism, where the thyroid is slightly underactive but not enough to cause obvious symptoms.
Each individual's situation can be unique, so it's always best to discuss test results with a
healthcare provider to get a complete understanding in the context of your overall health.