The panel provides an assessment of thyroid function and includes Thyroid Stimulating Hormone test.

Clinical Significance

This panel provides an assessment of thyroid function and includes tests for thyroid stimulating hormone (TSH), total thyroxine (T4), triiodothyronine (T3) uptake (T3 resin uptake), and free T4 index. This panel may be useful for evaluating thyroid function when pituitary disease is not suspected. The results of the panel may help in the diagnosis of hyperthyroidism and hypothyroidism.

T3 and T4 are hormones derived from the thyroid and released into the blood to regulate metabolism. Both T3 and T4 are produced in response to TSH from the pituitary gland. T4 circulates mostly bound to plasma proteins, with a small amount unbound and available for biological activity. To estimate free T4 concentration, a total T4 test and T3 uptake test are used to calculate the free T4 index.

A normal TSH result excludes most cases of primary overt thyroid disease. Therefore, a cascaded testing approach may be preferable for evaluating and monitoring thyroid function. This panel does not identify T3 thyrotoxicosis, which requires measurement of free T3.