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Free T4
Test CodeLAB127
Alias/See Also
FT4; Thyroxin Free
CPT Codes
84439
Instructions
"Routine venipuncture
Collect one 5ml Red/gold top serum separator tube"
Collect one 5ml Red/gold top serum separator tube"
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Moderate hemolysis; failure to follow proper collection or storage procedures
Methodology
Competitive Immunoassay:The amount of HRP conjugate bound is indirectly proportional to the concentration of FT4 present.
Setup Schedule
Daily/STAT
Report Available
within 24 hrs
Reference Range
0-10 days: 0.60-2.00 ng/dL10 days-20 years: 0.78-2.49 ng/dL20 years-40 years: 0.79-2.35 ng/dL 40 years-60 years: 0.64-1.79 ng/dL60 years-80 years: 0.78-2.44 ng/dLGreater than 80 years: 0.85-1.93 ng/dL
Clinical Significance
"Thyroxine is a hormone synthesized and secreted by the thyroid gland and plays an important role in regulating metabolism. Secretion into the circulation is in response to the pituitary hormone TSH and regulated by a negative feedback mechanism involving the thyroid gland, pituitary gland, and hypothalamus.
In the circulation, 99.95% of T4 is reversibly bound to transport proteins, primarily TBG (thyroid binding globulin). The remaining T4 is not bound to transport proteins, but is free in the circulation. This unbound fraction, or free T4, is both metabolically active and a precursor to T3.
Free T4 levels correlate with T4 secretion and metabolism. In hypothyroidism and hyperthyroidism, FT4 levels parallel changes in T4 levels. Free T4 levels are unchanged, while T4 levels will fluctuate with changes in TBG."
In the circulation, 99.95% of T4 is reversibly bound to transport proteins, primarily TBG (thyroid binding globulin). The remaining T4 is not bound to transport proteins, but is free in the circulation. This unbound fraction, or free T4, is both metabolically active and a precursor to T3.
Free T4 levels correlate with T4 secretion and metabolism. In hypothyroidism and hyperthyroidism, FT4 levels parallel changes in T4 levels. Free T4 levels are unchanged, while T4 levels will fluctuate with changes in TBG."
Additional Information
NCD-ABN_Thyroid_Testing
