Test Code T4FRER T4, Free LAB127
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.
Reference Values
Reference range established for patients > 18 yrs:
0.61-1.12 ng/dL
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.
LOINC Code Information
3024-7 Thyroxine (T4) Free [Mass/Volume] In Serum Or Plasma
Method
Two-Site Immunoassay; Beckman
CPT Information
84439: Chemistry: Thyroid Tests Thyroxine; Total free