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Free T3
Test CodeLAB137
Alias/See Also
FT3; Triiodothyronine Free
CPT Codes
84481
Instructions
"Routine venipuncture
Collect one 5ml Red/gold serum separator tube"
Collect one 5ml Red/gold serum separator tube"
Specimen Stability
Refrigerate, stable <72 hours; stable <24 hours at room temperature; stable 1 month if frozen
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Gross hemolysis or lipemia
Methodology
Competitive Immunoassay:The amount of HRP conjugate bound is indirectly proportional to the concentration of FT3 present.
Setup Schedule
Daily/STAT
Report Available
within 24 hrs
Reference Range
2.77-5.27 pg/mL
Clinical Significance
"The formation of triiodothyronine (T3) (about 80%) results from conversion of thyroxine (T4) to T3 in peripheral tissues. T3 is also synthesized by the follicular cells of the thyroid gland, which accounts for only about 20% of T3 levels. For the most part, free T3 levels correlate closely with total T3 levels. Total T3, however, is a function not only of thyroid status and the peripheral conversion of T4 to T3, but also of the concentration of thyroid hormone-binding proteins. Free T3, on the other hand, is largely unaffected by variations in these carrier proteins. Thus, the TBG elevations typical of pregnancy, oral contraceptives, and estrogen therapy will induce an increase in the total T3 level without affecting the free T3 concentration.
Measurement of total triiodothyronine (total T3) by immunoassay has a number of well-established uses. It is often employed to help confirm a diagnosis of hyperthyroidism where an elevated free or total thyroxine (T4) has been encountered. Abnormal elevations in total T3 may also occur in the context of a normal total T4 in a condition known as ""T3 toxicosis""."
Measurement of total triiodothyronine (total T3) by immunoassay has a number of well-established uses. It is often employed to help confirm a diagnosis of hyperthyroidism where an elevated free or total thyroxine (T4) has been encountered. Abnormal elevations in total T3 may also occur in the context of a normal total T4 in a condition known as ""T3 toxicosis""."
