radiolabeled iodine in the thyroid
5 hr – 5 to 15%
24 hr – 15 to 35%
Free T4 - much more useful then total T4 (e.g. interested in unbound
or active form). Total T4 not commonly measured. Greatly affected by
Free T4 index: indirect measure of free T4. Corrects for high/low
values of TBG.
Total T3: not as useful as free T3, however, may be useful in
locating problems with TBG, or if looking for problems with peripheral
conversion of T4 to T3.
Resin T3 Uptake: if low, then TBG binding capacity is high. Opposite
TSH: best measure to determine thyroid function.
Thyroglobulin: nonspecific test that is elevated when the thyroid
gland is inflamed or enlarged.
Normal: < 150 mg/dL. Borderline-high:
150 to 199 mg/dL High: 200 to 499 mg/dL Very High: >499 mg/dL
<2.26 mmol/L (<200 mg/dL)
>Unless noted, all values are for adults. >All laboratory values listed are method dependent
(Methods include: immunoassay, colorimetry, electrophoresis,
HPLC, etc). >Values may vary between laboratories.