This is to assess thyroid function, eg detect hyperthyroidism.
T3 is from 80% by deiodination of T4.
Some free T3 is present in the normal state in the blood: the majority is a TBG (thyroxine binding globulin).
Sampling 10 mL EDTA blood.
0.3 to 0.4 mU / L.
– In hypothyroidism:
– The first sign is the elevation of TSH greater than 20 mU / L, whereas free T4 is itself, diminished,
– The therapeutic goal is to obtain TSH levels less than 1 mU / L;
– In hyperthyroidism:
– The ultrasensitive TSH is low, less than 0.1 or 0.2 mU / L,
– Q3 rate is increased, that of T4 less.
Medications containing thyroid hormones may distort the results.
It is the same for those that contain iodine causing a diversion from the conversion of T4 to T3.