CPT® Code 84479

The CPT® Code 84479 refers to the measurement of thyroid hormone uptake, specifically for T3 (triiodothyronine) or T4 (thyroxine), which is also known as the thyroid hormone binding ratio (THBR). This procedure involves obtaining a blood sample from the patient to assess how well these thyroid hormones are being taken up by the body's tissues. The uptake of thyroid hormones is influenced by three key proteins: thyroid binding globulin (TBG), transthyretin, and albumin. These proteins bind to thyroid hormones, rendering them inactive in the bloodstream. The thyroid hormone uptake is expressed as a ratio, comparing the uptake in a solid matrix to the uptake in serum. This calculation of the THBR is crucial for physicians as it aids in identifying potential abnormalities in binding proteins that may affect thyroid hormone function. The test is conducted using an electrochemiluminescent immunoassay, a sensitive and specific method for measuring hormone levels in the blood.