Medical Biochemistry 2: Thyroid Function Test

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Questions and Answers

What is the primary cause of primary hyperthyroidism?

Insufficiency of iodine

Tumor of the pituitary gland

Infection of the thyroid gland

Autoimmune disease (correct)

What is the characteristic symptom of Graves' disease?

Exophthalmos (correct)

Joint pain

Weight gain

Shortness of breath

What is the name of the disease caused by the presence of thyroid-stimulating antibodies (TSA)?

Graves' disease (correct)

Plummer's disease

Chorionic gonadotropin secreting tumors

Thyroid hormone resistance syndrome

What is the typical age range for the development of toxic nodular goiter?

Over 60 years old Signup and view all the answers

What is the effect of thyroid-stimulating antibodies (TSA) on the thyroid gland?

Increase production of thyroid hormone Signup and view all the answers

What is the characteristic laboratory finding in primary hyperthyroidism?

Low TSH level and high free T4 level Signup and view all the answers

What is the name of the disease caused by the presence of areas that have increased in size and formed nodules in the thyroid gland?

Toxic nodular goiter Signup and view all the answers

What is the effect of thyroid hormone resistance syndrome on the thyroid gland?

Resistance to thyroid hormone Signup and view all the answers

What is the characteristic of primary hypothyroidism?

High TSH level and low free T4 level Signup and view all the answers

What is the common cause of congenital hypothyroidism?

Defects in the synthesis of thyroid hormone Signup and view all the answers

What is the consequence of untreated congenital hypothyroidism?

Severe impaired growth and permanent mental retardation Signup and view all the answers

What is the characteristic of secondary hypothyroidism?

Low TSH level and low free T4 level Signup and view all the answers

What is the main disadvantage of using total T4 (tT4) and total T3 (tT3) tests?

They can be affected by plasma binding protein levels Signup and view all the answers

What can cause an increase in thyroxine-binding globulin (TBG) levels?

Pregnancy and oral contraceptive pills containing estrogen Signup and view all the answers

Why can an increase in thyroxine-binding globulin (TBG) levels lead to a false positive diagnosis of hyperthyroidism?

Because it increases the binding of thyroid hormones to proteins Signup and view all the answers

What is the purpose of thyroid function tests?

To detect and diagnose thyroid disease, monitor response to treatment, and evaluate the prognosis of thyroid cancer Signup and view all the answers

Study Notes

Thyroid Function

Thyroid function tests are used to detect and diagnose thyroid disease, monitor response to treatment of thyroid disorders, and evaluate the prognosis of thyroid cancer.

Hypothyroidism

Primary hypothyroidism: underactive thyroid gland that produces insufficient amounts of thyroid hormones, characterized by high TSH level and low free T4 level.
Causes of primary hypothyroidism:
- Autoimmune mediated destruction of thyroid tissue (Hashimoto's thyroiditis)
- Thyroidectomy and radiation therapy
- Iodine deficiency in diet
Congenital hypothyroidism: babies with defects in thyroid hormone synthesis, absent thyroid gland, or TSH receptor mutation; can lead to severe impaired growth and permanent mental retardation (cretinism) if left untreated.

Hyperthyroidism

Primary hyperthyroidism: overactive thyroid gland leading to excessive synthesis of thyroid hormones (thyrotoxicosis), characterized by low TSH level and high free T4 level.
Causes of primary hyperthyroidism:
- Graves' disease: an autoimmune disease that stimulates thyroid hormone production.
- Toxic nodular goiter: enlargement of the thyroid gland with nodules, often occurs in older adults (over 60 years old) and is associated with iodine insufficiency.
- Functioning thyroid adenoma: a benign tumor of the thyroid gland.

Graves' Disease

An autoimmune disease that stimulates thyroid hormone production.
Characterized by:
- Presence of thyroid-stimulating antibodies (TSA) that bind to TSH receptors in the thyroid gland.
- Symptoms: exophthalmos (bulging eyes), goitre (thyroid enlargement), rapid pulse, weight loss, excessive sweating, and heat intolerance.

Thyroid Function Tests

Two standard tests used to profile thyroid function:
- Thyroid stimulating hormone (TSH)
- Free thyroxine (FT4)
Total T4 (tT4) and total T3 (tT3) have major disadvantages, such as false positive diagnosis of hyperthyroidism due to changes in thyroxine-binding globulin (TBG) levels.
TBG levels may be affected by:
- Pregnancy and oral contraceptive pills containing estrogen (may increase TBG levels)
- Protein-losing enteropathy, malnutrition, and malabsorption (may decrease TBG levels)

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Description

This quiz covers the conditions leading to abnormal thyroid hormone production and interpretation of thyroid function tests, including primary hyperthyroidism and its effects.