The T4 test is performed as part of an evaluation of thyroid function. Two blood tests may be performed as part of a T4 test: total T4, which measures the entire amount of thyroxine in the blood, including the amount attached to blood proteins that help transport the hormone through the bloodstream.

SPECIMEN: 2 mL (1 mL min.) serum from 1 SST. Ship refrigerated or frozen.
STABILITY: Room: 2 hrs; Refrigerated: 1 week; Frozen: 4 weeks
REPORT: Daily
INSTRUCTIONS: No special preparation required

USAGE: Total T4 levels offer a good index of thyroid function when TBG is normal and non-thyroidal illness is not present. This assay is useful for monitoring treatment with synthetic hormones (synthetic T3 will cause low total T4).It also helps to monitor treatment of Hyperthyroidism with Thiouracil or other anti-thyroid drugs.