Overview
This presentation explains thyroid function tests, including free T4, free T3, and TSH, describing how their interactions help diagnose thyroid health, including hyperthyroidism and hypothyroidism.
The Thyroid and Pituitary Glands
- The thyroid is a butterfly-shaped gland at the base of the neck responsible for producing thyroid hormones T4 and T3.
- The pituitary gland, located at the base of the brain, monitors and regulates thyroid activity.
- The pituitary releases thyroid stimulating hormone (TSH) to control thyroid hormone production.
Thyroid Hormones and Their Regulation
- TSH stimulates the thyroid to grow and produce T4 and T3 hormones.
- As thyroid hormone levels in the blood change, the pituitary adjusts TSH production to maintain hormonal balance.
- This relationship is likened to a thermostat (pituitary) controlling a furnace (thyroid) or a teeter totter balancing T4/T3 and TSH.
Interpreting Thyroid Function Tests
- High T4/T3 with low TSH suggests hyperthyroidism (overactive thyroid).
- Low T4/T3 with high TSH indicates hypothyroidism (underactive thyroid).
- TSH is typically used as the initial screening test for thyroid conditions.
Hyperthyroidism
- Overproduction of thyroid hormones leads to reduced TSH as the pituitary tries to decrease hormone output.
- Providers often diagnose an overactive thyroid when TSH is low.
Hypothyroidism
- Underproduction of thyroid hormones results in increased TSH as the pituitary attempts to stimulate hormone production.
- Elevated TSH is a typical marker for an underactive thyroid.
Summary and Takeaways
- T4 and T3 are the main thyroid hormones; TSH reflects the pituitary's regulatory response.
- When all values are normal, the thyroid system is balanced.
- The teeter totter analogy helps visualize the inverse relationship between T4/T3 and TSH in diagnosing thyroid health.