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Free Thyroxine Index (N/A)
Test Mnemonic:


Specimen Requirements:

Routine venipuncture

AM collection preferred.  Preferred: 7 mL SST (gel barrier) tube; Acceptable: 7 mL red topped tube (see storage instructions) . (Min.: 3mL of blood).

Minimum Volume:

3 mL of blood


Delivered to Sample Management within 2 hours of collection.   

Specimen Preparation:

Allow specimen to clot completely at room temperature. Centrifuge to separate serum from cells within 2 hours of collection. Transfer serum from collection tube to labeled plastic transport tube. 

Causes for Rejection:

Incomplete and/or incorrect sample identification, improper storage/transport, and gross hemolysis and lipemia. 

Reference Range:
Turnaround Time:

Routine: 8 hours; ASAP: 4 hours




24 hours a day; 7 days a week


Clinica Chemistry

Patient Preparation :

AM collection preferred.

CPT 4 Code:

See individual tests.

When ordering tests for which Medicare or Medicaid reimbursement will be sought, physicians should only order tests that are medically necessary for the diagnosis or treatment of the patient. Components of the organ or disease panels may be ordered individually. The diagnostic information must substantiate all tests ordered and must be in the form of an ICD-10 code or its verbal equivalent.
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