Triiodothyronine (T3) normally represents only approximately 5% of the thyroid hormone and like thyroxine is almost entirely bound to the carrier proteins, with only 0.25% of the total being in the free state. Measurement of free triiodothyronine is of value in confirming the diagnosis of hyperthyroidism, when an elevated free or total thyroxine level is found. Abnormal total and free triiodothyronine concentrations may appear in T3 toxicosis, in the presence of normal thyroxine levels. Free T3 levels are unaffected by carrier protein variation. - Free thyroxine (FT4) comprises a small fraction of total thyroxine. The FT4 is available to the tissues and is, therefore, the metabolically active fraction. Elevations in FT4 cause hyperthyroidism, while decreases cause hypothyroidism.
Inform your doctor if you are on any medications, have any allergies or underlying medical conditions before your FT3 and FT4. Your doctor will give specific instructions depending on your condition on how to prepare for FT3 and FT4.
10 to 12 Hours fasting is required before the sample collection.
|MALE||All age groups||1.8 - 5.4mcg/dl|
|FEMALE||All age groups||1.8 - 5.4mcg/dl|
|MALE||All age groups||4.5 - 11.7 mcg/dl|
|FEMALE||All age groups||4.5 - 11.7 mcg/dl|