T4, Total (Thyroxine)

CPT: 84436



Expected Turnaround Time

24 Hours

Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.

Specimen Requirements


Serum, Plasma


SST (Serum), Red Top (Separate Serum), Lithium Heparin (Plasma)

Storage Instructions

Room Temp., Refrigerated (2-8 C)

Stability Requirements

Room temp. 72hrs., Refrigerated 7 days

Test Details

Additional Information

T4 (thyroxine) total test is the one that checks the blood levels of the T4 hormone produced by the thyroid gland. The thyroid gland is one of the largest endocrine glands of the body, weighing about 15g to 20g in adults, present in front of the lower neck. It produces triiodothyronine and tetraiodothyronine or thyroxine, commonly known as T3 and T4 hormones, respectively. 

These hormones serve in the major functioning of the body like growth, muscle strength, and special increment of the body’s metabolism. A deficiency of thyroid hormones decreases the body’s metabolism by up to 40 to 50 percent. These hormones are secreted from the thyroid gland after being stimulated by TSH (thyroid-stimulating hormone), released by the master endocrine gland, the pituitary gland. 

About 93% of the thyroid hormones released are T4, and 7% are T3. The thyroid gland also secretes another hormone, calcitonin, which maintains the blood and bone calcium balance of the body. 

T4 (thyroxine) total test is used to diagnose many thyroid dysfunctions. This test measures total T4 levels (either bound or free) in the blood. 

Abnormally high T4 levels indicate an increment in the size of the thyroid gland due to hyperplasia (increased cell division), which results in more production and secretion of T4. This is what usually causes hyperthyroidism. 

Opposite to that, low T4 levels are possible because of the deterioration of the thyroid gland resulting in low amounts of T4, leading to hypothyroidism. 

Some autoimmune diseases can also cause both conditions based on whether they stimulate the thyroid gland or destroy it. 



  1.  Thyroxine (T4) Test: MedlinePlus Lab Test Information [accessed on Oct 2, 2018]  
  2. T4 – Clinical: T4 (Thyroxine), Total Only, Serum [accessed on Oct 2, 2018]   


Statement on Medical Necessity
All ordered tests should be medically necessary for the diagnosis or detection of disease, illness, impairment, symptom, syndrome, or disorder and the results should be used in the medical management and treatment decisions for the patient. Solaris requires ICD-10 codes with each order for lab testing and both the tests ordered and the diagnosis should be documented in the provider’s medical record for the patient. The United States Department of Health and Human Services, Office of Inspector General, takes the position that a provider who orders medically unnecessary tests may be subject to civil penalties.

Panels and Profiles
Solaris offers Providers the convenience of ordering test combinations in a group at times with the flexibility to choose appropriate test(s) for individual patients. Providers should only order those tests that he or she believes are medically necessary for each patient, and a lesser inclusive profile or individual tests should be ordered if not all tests in the test combination/profile are medically necessary. All tests offered in a test combination/profile may be ordered separately as individual tests. Solaris encourages clients to contact their Solaris representative if the testing configurations shown do not meet individual needs for any reason, or if some other combination of procedures is needed.

CPT Codes
CPT Codes listed are in accordance with Current Procedural Terminology, a publication of the American Medical Association. CPT codes are the responsibility of the billing party and are listed here for informational purposes. Correct coding may vary from one carrier to another. Solaris may bill specific carriers using codes other than what is shown.


For questions or inquiries related to testing please reach out to
customerservice@solarisdx.com or contact us by phone at (844) 550-0308.