Thyroxine (T4, Total)
Test name: Thyroxine (T4, Total)
Order Code: T4
Preferred Specimen: 2mL serum in a Serum Separator Tube (SST or Tiger-top)
CPT Code: 84436
Collection: Allow SST to clot in an upright position for 30 min, then centrifuge sample within 2 hours of collection. Refrigerate.
Special Instructions and Considerations: 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. Binding protein anomalies seen with FDH (familial dysalbuminemic hyperthyroxinemia), for example, may cause values which, while characteristic of the condition, deviate from the expected results.
Transport Temperature: Refrigerated
Specimen Stability: 7 days refrigerated