TSH
Overview
TSH (thyroid-stimulating hormone) measures pituitary gland secretion that regulates thyroid hormone production, assessing the hypothalamic-pituitary-thyroid axis feedback loop. It stimulates thyroid follicular cells to produce thyroxine (T4) and triiodothyronine (T3), maintaining metabolic rate, growth, and thermogenesis. High TSH indicates primary hypothyroidism, while low TSH suggests hyperthyroidism or central hypothyroidism; it serves as the primary screening test for thyroid dysfunction due to its sensitivity in detecting subclinical disease before T4/T3 abnormalities occur.
Clinical Use Cases
- Screening for hypothyroidism and hyperthyroidism.
- Monitoring levothyroxine replacement therapy.
- Diagnosing subclinical thyroid disease.
- Evaluating pituitary function (central hypothyroidism).
- Assessing thyroiditis or toxic nodule suppression.
Specimen Types
- Serum.
- Plasma (heparin).
Measurement Methods
- Third-generation immunometric assays (sandwich ELISA).
- Chemiluminescent immunoassays.
- Electrochemiluminescent assays.
Test Preparation and Influencing Factors
- Morning collection preferred (slight diurnal variation).
- No fasting required.
- Avoid biotin supplements (interfere with assays).
- Non-thyroidal illness syndrome lowers TSH.
- Pregnancy, age, medications (amiodarone, glucocorticoids) alter levels.
Synonyms
- Thyrotropin.
- hTSH.