Free T4 is a useful tool in clinical routine diagnostics for the assessment of the thyroid status. It should be measured together with TSH if thyroid disorders are suspected and is also suitable for monitoring thyrosuppressive therapy
Samples should not be taken from patients receiving therapy with high biotin doses (i.e. > 5 mg/day) until at least 8 hours following the last biotin administration.
The test cannot be used in patients receiving treatment with lipid-lowering agents containing D‑T4. If the thyroid function is to be checked in such patients, the therapy should first be discontinued for 4‑6 weeks to allow the physiological state to become re-established. Autoantibodies to thyroid hormones can interfere with the assay
Refrigerated: 7 days Frozen: 1 month
Free T4; T4, free
Serum, gel separator, SST
0 - 999
0.93 ng/dL - 1.7 ng/dL