Free Triiodothyronine (T3) and Reverse T3

POLICY NUMBER

L.2.04.406

DESCRIPTION

Thyroid hormones regulate a number of developmental, metabolic, and neural activities throughout the body. The 2 main hormones secreted by the thyroid gland are thyroxine, which contains 4 atoms of iodine (Thyroxine [T4]), and triiodothyronine (T3). T3 is also produced by conversion (deiodination) of T4 in peripheral tissues. Circulating levels of T4 are much greater than T3 levels, but T3 is more metabolically active than T4, although its effect is briefer. Measurment of thyroid stimulating hormone (TSH) and T4 are addressed in a separate medical policy,  Thyroid Studies . 

Diagnosis of Hyperthyroidism

Serum TSH measurements are useful for the diagnosis of hyperthyroidism, but they are unable to distinguish the degree of hyperthyroidism since suppression occurs in the early stages of the disease. T3 tests are often useful to diagnosis hyperthyroidism or to determine the severity of the hyperthyroidism. The T3 test is usually ordered following an abnormal TSH and T4 test. Either the total T3 or the free T3 may be ordered. Since most of the T3 is bound to protein, the total T3 can be affected by protein levels and protein binding ability, but the free T3 is not. T3 testing may be ordered along with thyroid antibodies to help diagnose Graves disease, an autoimmune disorder that is the most common cause of hyperthyroidism.

During the early treatment of hyperthyroidism, serum TSH may remain subnormal for several weeks and rarely for several months. One must therefore rely upon serum free T4 and T3 measurements when assessing the efficacy of antithyroid drugs, radioiodine, or surgery. Once steady-state conditions are assured, measurement of serum TSH is required to assess the efficacy of therapy. In hyperthyroidism, both T4 and T3 levels are usually elevated, but in a small subset of hyperthyroid patients only T3 is elevated (T3 toxicosis). Serum T3 concentrations are disproportionately higher than serum T4 concentrations in many types of hyperthyroidism. As a result, serum T3 measurements may be valuable for evaluating and following patients with this disorder.

Common signs and symptoms of hyperthyroidism include heart palpitations, increased heart rate, intolerance to heat, nervousness, insomnia, breathlessness, increased bowel movements, light or absent menstrual periods, fatigue, trembling hands, weight loss, muscle weakness, hair loss, and warm, moist skin.

Amiodarone and Thyroid Dysfunction

Amiodarone, a class III anti-arrhythmic drug, has multiple effects on myocardial depolarization and repolarization that make it an extremely effective antiarrhythmic drug. However, amiodarone is associated with a number of side effects, including thyroid dysfunction (both hypo- and hyperthyroidism), which is due to amiodarone's high iodine content and its direct toxic effect on the thyroid. Amiodarone inhibits outer ring 5'-monodeiodination of T4, thus decreasing T3 production; reverse T3 accumulates since it is not metabolized to T2.Amiodarone, and particularly the metabolite desethylamiodarone, blocks T3-receptor binding to nuclear receptors and decreases expression of some thyroid hormone-related genes.Amiodarone may have a direct toxic effect on thyroid follicular cells, which results in a destructive thyroiditis. 

POLICY

Measurement of free T3 is considered medically necessary to confirm a diagnosis of hyperthyroidism if the following criteria are met:

1. There is clinical suspicion of hyperthyroidism (see Policy Guidelines) AND

2. TSH is low AND

3. T4 is normal or low

Follow-up measurement of free T3 is considered medically necessary after treatment for hyperthyroidism to assess the efficacy of antithyroid drugs, radioactive iodine 131, or thyroid surgery.

Measurement of freeT3 is considered notmedically necessary for evaluation and management of primary hypothyroidism.

Measurement of reverse T3 is considered medically necessary in patients taking amiodarone.

Measurement of free T3 or reverse T3 is considered not medically necessary for general screening without a clinical suspicion of hyperthyroidism.

POLICY EXCEPTIONS

None

POLICY GUIDELINES

The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.

Symptoms of hyperthyroidism may stem from many organ systems or an increase in adrenergic tone and include the following:

• palpitations/arrhythmias

• fatigue

• heat intolerance/sensitivity

• increased sweating

• exertional intolerance

• proximal or general muscle weakness

• thirst

• pruritus

• insomnia

• hair loss, hair thinning

• nervousness, restlessness, anxiety, irritability

• emotional lability

• inability to concentrate

• depression

• tremor

• goiter

• dyspepsia

• frequent bowel movements (hyperdefecation)

• increased appetite

• weight loss (loss of lean muscle and body fat despite increased appetite and food intake)

• change in appearance, swelling of eyelids or protrusion of eye, lid retraction

• irregular menses

• amenorrhea

• decreased libido

• hyperactive reflexes

Medically Necessary is defined as those services, treatments, procedures, equipment, drugs, devices, items or supplies furnished by a covered Provider that are required to identify or treat a Member's illness, injury or Mental Health Disorders, and which Company determines are covered under this Benefit Plan based on the criteria as follows in A through D:

A.  consistent with the symptoms or diagnosis and treatment of the Member's condition, illness, or injury; and

B.  appropriate with regard to standards of good medical practice; and

C.  not solely for the convenience of the Member, his or her Provider; and

D.  the most appropriate supply or level of care which can safely be provided to Member. When applied to the care of an Inpatient, it further means that services for the Member's medical symptoms or conditions require that the services cannot be safely provided to the Member as an Outpatient.

For the definition of medical necessity, “standards of good medical practice” means standards that are based on credible scientific evidence published in peer-reviewed medical literature generally recognized by the relevant medical community, and physician specialty society recommendations, and the views of medical practitioners practicing in relevant clinical areas and any other relevant factors. BCBSMS makes no payment for services, treatments, procedures, equipment, drugs, devices, items or supplies which are not documented to be Medically Necessary. The fact that a Physician or other Provider has prescribed, ordered, recommended, or approved a service or supply does not in itself, make it Medically Necessary.

POLICY HISTORY

10/01/2013: New policy added.

07/22/2014: Added ICD-9 codes 244.0 and 244.1 to the Code Reference section.

08/28/2015: Medical policy revised to add ICD-10 codes. ICD-9 diagnosis code 780.7 extended to the fifth digit (780.79).

06/07/2016: Policy number L.2.04.406 added. Policy Guidelines updated to add medically necessary definition.

09/30/2016: Code Reference section updated to add new ICD-10 diagnosis codes F34.81 and F34.89.

09/29/2017: Code Reference section updated to add new ICD-10 diagnosis code R06.03, effective 10/01/2017. Removed deleted ICD-10 diagnosis code F34.8.

05/30/2018: Deleted outdated references in Sources section.

10/01/2021: Code Reference section updated to add new ICD-10 diagnosis code F32.A.

10/14/2022: Policy reviewed. Policy statements unchanged. Policy Guidelines updated to change "Nervous/Mental Conditions" to "Mental Health Disorders" and "Medically Necessary" to "medical necessity."

09/29/2023: Code Reference section updated to add new ICD-10 diagnosis codes I47.10, I47.11, and I47.19, effective 10/01/2023.

10/18/2023: Policy reviewed; no changes.

12/04/2024: Policy reviewed; no changes.

SOURCE(S)

1. DynaMed - Graves disease

2. DynaMed - Hyperthyroidism

3. DynaMed - Toxic multinodular goiter

4. DynaMed - Toxic thyroid adenoma

5. Endocrine Physician Advisory Committee

6. http://labtestsonline.org/understanding/analytes/t3/tab/test

7. http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/8613

8. Thyroid Function Tests. American Thyroid Association-

   http://thyroid.org/wp-content/uploads/patients/brochures/FunctionTests_brochure.pdf

9. UptoDate® - Diagnosis of hyperthyroidism

10. UptoDate® - Amiodarone and thyroid dysfunction

CODE REFERENCE

This may not be a comprehensive list of procedure codes applicable to this policy.

The code(s) listed below are ONLY medically necessary if the procedure is performed according to the "Policy" section of this document.

Covered Codes

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