Thyroxine (T4), Total

Cleveland Heartlab T, Test, Thyroid Function

CPT Code: 84436
Order Code: C158
ABN Requirement:  No
Synonyms: Total T4; T4
Specimen: Serum
Volume: 0.5 mL
Minimum Volume: 0.2 mL
Container: Gel-barrier tube (SST, Tiger Top)


  1. Collect and label sample according to standard protocols.
  2. Gently invert tube 5 times immediately after draw. DO NOT SHAKE.
  3. Allow blood to clot 30 minutes.
  4. Centrifuge for 10 minutes.

Special Instructions: Samples should not be taken from patients receiving therapy with high biotin doses (>5 mg/day) until at least 8 hours following the last dose. Patients receiving treatment with lipid-lowering agents containing D-T4 should stop treatment for 4-6 weeks prior to collecting the sample.

Transport: Store serum at 2°C to 8°C after collection and ship the same day per packaging instructions provided with the Cleveland HeartLab shipping box.


Ambient (15-25°C): 4 days
Refrigerated (2-8°C): 8 days
Frozen (-20°C): 12 months
Deep Frozen (-70°C): 12 months

Causes of Rejection: Samples which are heat-inactivated; specimens other than serum; improper labeling; samples not stored properly; samples older than stability limits

Methodology: Electrochemiluminescence Immunoassay (ECLIA)

Turn Around Time: 1 to 5 days

Reference Range:

Age ug/dL
0-7 days 8.2-21.5
8-30 days 7.2-15.6
31 days – 1 year 7.2-15.6
≥2 years 4.5-11.7


Intended Use: A total thyroxine test may be ordered for the evaluation of thyroid function but its utility is less than measurement of Free Thyroxine.

Limitations: Autoantibodies to thyroid hormones can interfere with the assay. Binding protein anomalies seen with FDH (familial dysalbuminemic hyperthyroxinemia), for example, may cause values which, while characteristic of the condition, deviate from the expected results. In rare cases, interference due to extremely high titers of antibodies to analyte-specific antibodies, streptavidin or ruthenium can occur.

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 payer being billed.