Test Code T4FRER T4, Free LAB127
Performance
Testing is performed Monday through Sunday.
Routine: Typically completed within 4 hours after the specimen arrives at the testing site.
STAT: Typically completed within 1.5 hours after the specimen arrives at the testing site.
Useful For
The test generally is used as a second-line test after thyroid-stimulating hormone (TSH) to help evaluate TSH changes.
The Free Thyroxine value, combined with the TSH value, gives a more accurate picture of the thyroid status in patients with abnormal thyroid-binding globulin levels such as those who are pregnant or those who are receiving treatment with estrogens, androgens, phenytoin, or salicylates.
Specimen Requirement
0.5 mL serum or plasma is required.
Collect blood in a lithium heparin, green-top or red-top tube. PST and SST (gel tubes) are acceptable. Serum or plasma should be separated from contact with the cells within 2 hours of collection. Specimens not centrifuged within 4 hours of collection may be rejected. Refrigerate the specimen if unable to assay within 8 hours of collection.
Method
Two-Site Immunoassay; Beckman
Reference Values
Reference range established for patients > 18 yrs:
0.61-1.12 ng/dL
CPT Information
84439: Chemistry: Thyroid Tests Thyroxine; Total free
LOINC Code Information
3024-7 Thyroxine (T4) Free [Mass/Volume] In Serum Or Plasma