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DESCRIPTIONThyroid 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.
POLICYMeasurement of free T3 is considered medically necessary to confirm a diagnosis of hyperthyroidism if the following criteria are met:
Follow-up measurement of free T3 is considered medically necessary after treament for hyperthyroidism to assess the efficacy of antithyroid drugs, radioactive iodine 131, or thyroid surgery.
Measurement of freeT3 is considered not medically 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 revervse T3 is considered not medically necessary for general screening without a clinical suspicion of hyperthyroidism.
POLICY GUIDELINESSymptoms of hyperthyroidism may stem from many organ systems or an increase in adrenergic tone and include the following:
Investigative service is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized by certifying boards and/or approving or licensing agencies or published peer review criteria as standard, effective medical practice for the treatment of the condition being treated and as such therefore is not considered medically necessary.
The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.
POLICY HISTORY10/01/2013: New policy added.
CODE REFERENCEThis 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.