Test Code: 35167
CPT Code(s): 84439
Methodology: Direct Equilibrium Dialysis Radioimmunoassay (RAI)
Laboratory Developed Test (LDT) - This was developed and its analytical performance characteristics have been deteremined by Quest Diagnostics Nichols Institute, Chantilly, VA. It has not been cleared or approved by the FSA. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.
Clinical Significance: Free T4 by equilibrium dialysis is the most accurate measure of Free T4. Results are independent of the concentration of the T4-binding proteins, the presence of molecular variants of these proteins, or circulating autoantibodies. Free T4 is useful in distinguishing euthyroidism from thyroid disease.
Additional names: Direct Free T4; Free T4 by Equilibrium Dialysis; Free T4 Direct Dialysis; T4 Free by Direct Dialysis; Thyroxine, Free by Direct Dialysis
Supply: #T157 Red/Yellow SST 8mL
Preferred Specimen: Serum
Preferred Volume: 1mL
Transport Container: Serum Separator Tube (SST)
Transport Temperature: Room Temperature
Special Instructions: Please specify on the request form the patient's age.
Specimen Stability: Room Temperature: 4 Days
Reject due:
- EDTA plasma
- Heparin plasma
- Hemolysis
- What are hemolyzed specimens?
- Hemolysis occurs when the red cells are damaged during sample collection causing them to rupture. Hemolyzed serum or plasma is pale pink to red rather than the normal clear straw or pale-yellow color.
- What causes a specimen to be hemolyzed?
- Mixing tubes too vigorously
- Placing tubes in the refrigerator without allowing 30 minutes at room temperature for complete clotting
- Exposure to heat or in a refrigerator that is too cold
- Using a needle with too small of a bore necessary for the venipuncture
- Using too large a tube when using a butterfly needle
- Not allowing sufficient time for alcohol to dry on puncture site
- Leaving the tourniquet on for longer than one minute
- How can hemolyzed specimens be prevented?
- For routine collections, use a 20–22-gauge needle
- Do not remove the needle from the vein with the vacuum tube engaged
- Do not collect a specimen in a hematoma
- Do not centrifuge the specimen for a prolonged period of time
- Draw the sample gently and evenly
- What are hemolyzed specimens?
- Lipemia
- Specimens exceeding stability
- Specimens other than serum
- Unlabeled or improperly labeled specimens
For additional supply or collection information, please contact DLO's Customer Service at (800) 891-2917, option 2.
The CPT codes provided are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed.