Thyroid Panel with Thyroid-Stimulating Hormone (TSH): Thyroid function is critical to your metabolism and affects your energy level, heart rate, weight control, and more. The thyroid-stimulating hormone is produced in the pituitary gland and stimulates the production of thyroid hormones. The TSH helps identify an underactive or overactive thyroid state. This comprehensive evaluation of your thyroid hormone levels includes T-3 Uptake, T4, and Thyroid-Stimulating Hormone (TSH).
Free T3: Free T3 is for evaluating thyroid function and assessing abnormal binding protein disorders.
Free T4: Free T4 may be indicated when binding globulin (TBG) problems are perceived, or when conventional test results appear to be inconsistent with clinical observations. It is normal in those with high thyroxine-binding globulin hormone binding who are euthyroid (i.e., free thyroxin should be normal in nonthyroidal diseases). It should also be normal in familial dysalbuminemic hyperthyroxinemia.
Thyroid Peroxidase (TPO) Antibodies: Antibodies to thyroid microsomes (thyroid peroxidase) are present in 70% to 90% of patients with chronic thyroiditis. They are also present in smaller percentages of patients of other thyroid diseases. Antibody production may be confined to lymphocytes within the thyroid, and serum may be negative. Small numbers (3%) of people with no evidence of disease may have antibodies. This is more frequent in females and increases with age.
Thyroid Antithyroglobulin Antibody: This test may be ordered to investigate the cause of an enlarged thyroid gland (goiter) or performed as a follow-up when other thyroid test results (such as T3, T4, and TSH) show signs of thyroid dysfunction. One or more thyroid antibody tests also may be ordered if a person with a known non-thyroid-related autoimmune condition, such as rheumatoid arthritis, systemic lupus erythematosus, or pernicious anemia, develops symptoms that suggest thyroid involvement. Such involvement may occur at any time during the course of the other condition(s).
Reverse triiodothyronine (rT3): RT3 is an isomer of triiodothyronine (T3) with no demonstrated biological activity. The majority of rT3 is produced through peripheral enzymatic monodeiodination of T4 at the five positions of the inner ring of the iodothyronine nucleus of thyroxine (T4). A lesser amount of rT3 is secreted directly by the thyroid gland. T3 is biologically inactive and does not stimulate thyroid hormone receptors. Concentrations are elevated in chronic or acute diseases because of changes in peripheral rates of conversion of T4 to T3 and reverse T3. Drugs such as amiodarone and glucocorticoids cause increased levels of reverse T3. Reverse T3 levels are elevated at birth and will decline to normal levels by the first week of life. Measurement of reverse T3 may be of use in the assessment of thyroid function and metabolism in the newborn.
Thyroxine-binding Globulin (TBG): TBG distinguishes between high T4 levels due to hyperthyroidism and due to increased binding by TBG in euthyroid individuals who have normal levels of free hormones; document cases of hereditary deficiency or increase of TBG; work-up of thyroid disease. In patients with low T4, high T3 (uptake), or the reverse, who clinically seem eumetabolic and have normal FTI, measurement of TBG is only occasionally needed. Some such patients may have genetic anomalies of TBG. TBG is increased by estrogens, tamoxifen, pregnancy, perphenazine, and in some cases of liver disease, including hepatitis. Decreased TBG is found with some instances of chronic liver disease, nephrosis, and systemic disease, and with large amounts of glucocorticoids, androgens/anabolic steroids, and acromegaly. Although alterations of TBG are usually resolved by the thyroid profile, TBG must occasionally be directly measured.