Thyroid function tests Flashcards
What is the function of thyroid hormones?
Thyroid hormones regulate metabolism and are controlled by the hypothalamus and pituitary gland. The release of T3 and T4 is regulated through a negative feedback loop.
How is thyroid hormone production regulated?
The hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the anterior pituitary to release thyroid-stimulating hormone (TSH). TSH stimulates the thyroid gland to produce T3 and T4. The levels of T3 and T4 suppress TRH and TSH release via negative feedback.
What is negative feedback in thyroid hormone regulation?
Negative feedback occurs when elevated levels of thyroid hormones (T3 and T4) suppress the release of TRH and TSH, reducing thyroid hormone production to maintain normal levels.
What is the role of the TSH test?
The TSH test is used as a screening test for thyroid disease, helping determine whether thyroid hormone levels are abnormal.
What are the main causes of primary hyperthyroidism?
The main causes can be remembered using the ‘GIST’ mnemonic:
* Graves’ disease
* Inflammation (thyroiditis)
* Solitary toxic thyroid nodule
* Toxic multinodular goitre
What are the hormone levels in primary hyperthyroidism?
In primary hyperthyroidism:
* TSH is low
* T3 and T4 are high
What is secondary hyperthyroidism?
Secondary hyperthyroidism occurs when the pituitary gland produces excessive TSH, stimulating the thyroid to produce excess thyroid hormones.
What are the hormone levels in secondary hyperthyroidism?
In secondary hyperthyroidism:
* TSH is high
* T3 and T4 are high
What is primary hypothyroidism?
Primary hypothyroidism occurs when the thyroid gland produces insufficient thyroid hormones, leading to elevated TSH levels.
What are the causes of primary hypothyroidism?
Common causes include:
* Hashimoto’s thyroiditis
* Iodine deficiency
* Treatments for hyperthyroidism
What are the hormone levels in primary hypothyroidism?
In primary hypothyroidism:
* TSH is high
* T3 and T4 are low
What is secondary hypothyroidism?
Secondary hypothyroidism occurs when the pituitary gland produces insufficient TSH, leading to under-stimulation of the thyroid.
What are the hormone levels in secondary hypothyroidism?
In secondary hypothyroidism:
* TSH is low
* T3 and T4 are low
What are anti-thyroid peroxidase (anti-TPO) antibodies?
Anti-TPO antibodies are antibodies against the thyroid gland, commonly found in autoimmune thyroid diseases.
What are anti-thyroglobulin (anti-Tg) antibodies?
Anti-Tg antibodies are antibodies against thyroglobulin, a protein produced by the thyroid, and may be elevated in certain thyroid diseases.
What are TSH receptor antibodies?
TSH receptor antibodies mimic TSH and bind to TSH receptors, stimulating thyroid hormone release.
How is ultrasound used in thyroid evaluation?
Ultrasound helps diagnose thyroid nodules and distinguishes between cystic and solid nodules.
What is the role of radioisotope scans in thyroid evaluation?
Radioisotope scans investigate hyperthyroidism and thyroid cancers by measuring radioactive iodine uptake by the thyroid.
What does diffuse high uptake of radioactive iodine indicate?
Diffuse high uptake indicates Graves’ disease, where the entire thyroid is overactive.
What does focal high uptake of radioactive iodine indicate?
Focal high uptake suggests a toxic multinodular goitre or adenomas, where only part of the thyroid is overactive.
What do ‘cold’ areas in a radioisotope scan indicate?
‘Cold’ areas with abnormally low iodine uptake may indicate thyroid cancer.
