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Basic Thyroid Panel
Free Triiodothyronine (FT3)
Free Thyroxine (FT4)
Thyroid Stimulating Hormone (TSH)
 

Panels › Hormone Panels › Free Triiodothyronine (FT3)

Free Triiodothyronine (FT3)

Significance
Triiodothyronine (T3) is one of the two hormones produced by the thyroid gland. Like T4, its production is stimulated by secretion of TSH. Thyroid hormones have profound effects on important processes in the body such as development, growth, carbohydrate metabolism and lipid metabolism. Thyroid hormones also have effects on the cardiovascular system (heart rate, contractility), central nervous system (mental state) and the reproductive systems (infertility in hypothyroidism). T3 is mostly bound to Thyroid binding globulin with a small fraction bound to albumin. Only a small portion (<0.3%) is unbound (free form). T3 levels are lower but it is a more potent hormone than T4, and it has a longer half-life. Measurement of T3 is most commonly used to establish/rule out diagnosis of hyperthyroidism where its elevation occurs earlier and it is more pronounced. Levels are elevated in hyperthyroidism, Graves disease, and with T3 thyrotoxicosis (normal T4). Levels are often normal in hypothyroidism or in iodine deficiency. The free fraction, which is active form, is independent of variations in binding proteins and remains relatively constant.

Analysis
Determination of FT3 is performed by Enzyme Immunoassay.

Patient Preparation
Where appropriate and possible, avoid taking thyroid medication 48 hrs prior to specimen collection.

Specimen requirements
Serum specimen - from a plain redtop or a redtop gel (tiger top) tube. Separate serum from cells after centrifugation, if a plain redtop tube is used. Minimum volume required is 1 mL. Specimen should be kept refrigerated where possible.

Shipping Instructions
Ship specimen at ambient temperatures if transit time <24hrs. For longer times, ship refrigerated.

Additional information
http://www.labtestsonline.org/understanding/analytes/t3/test.html