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Test Code FT4 Free T4 Level

Important Note

Medicare frequency limitations exist for this test in addition to diagnosis requirements. Click on link for list of medically necessary diagnoses: http://www.munsonhealthcare.org/medical-necessity. Click on link for Advance Beneficiary Notice of Noncoverage form: Advance Beneficiary Notice of Noncoverage

EHR Test Codes

  Test Code Test Name
Atlas FT4 Free T4
Cerner FT4 Free T4 Level

Specimen Requirements

Preparation of Patient: 

None

 

Container Type: 

Green Top 5mL Lithium Heparin Separator Tube

Or

 

Gold Top 6mL SST Gel & Clot Activator Tube

Specimen Type:

Plasma or Serum

 

Specimen Volume: 

2.5 mL Plasma or Serum minimum .5 mL

 

Specimen Handling/Transport:

Separate plasma or serum from cells within 2 hours of collection.

Transport ambient room temperature.

 

Specimen Stability/Storage:

5 day refrigerated 2-8°C

Performing Laboratory

Munson Medical Center Laboratories

Chemistry Department

Priority, Frequency, & Turnaround

Priority:

Non-Emergent

 

Frequency:

24 hours 7 days a week

 

Turnaround:

0 - 1 days

Methodology

Chemiluminescence Immunoassay

Reporting

Reference Range:

 0.7 - 2 ng/dL

 

Interpretive Data:
Biotin supplements may falsely increase this analyte.

 

Critical Decision:

None

Clinical Significance

Thyroxine (T4) circulates in blood either protein bound or free. If thyroxine is bound, it is bound to thyroxine binding globulin (TBG), albumin or prealbumin. 99.97% of T4 is bound, the other 0.03% is free. Free T4 (FT4) is the physiologically active form. FT4 exists in an equilibrium state. As FT4 is absorbed by target cells or as the affinity of binding proteins changes, the FT4 equilibrium is reestablished. The target cells are therefore assured of a constant amount of hormone. Since FT4 is therefore less sensitive to changes in binding proteins, FT4 appears to be the best indicator of thyroid function.

CPT Code(s)

84439 

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