Thyroid Function Cascade, Serum

Use

This test utilizes a cascaded testing approach to efficiently evaluate and monitor functional thyroid status. The cascade begins with thyrotropin (TSH, formerly thyroid-stimulating hormone) as a screening assay. In patients with an intact pituitary-thyroid axis, TSH provides a physiologic indicator of the functional level of thyroid hormone activity. Increased TSH indicates inadequate thyroid hormone, and suppressed TSH indicates excess thyroid hormone. Transient TSH abnormalities may be found in seriously ill, hospitalized patients, so this is not the ideal setting to assess thyroid function. However, even in these patients, TSH works better than total T4 (thyroxine, an alternative screening test). When TSH is normal, no additional testing will be necessary. However, when the TSH result is abnormal, appropriate follow-up tests will automatically be performed.