Primary hypothyroidism is the most common cause of hypothyroidism, accounting for 99% of all cases.

Primary hypothyroidism is the most common cause of hypothyroidism, accounting for 99% of all cases.

1. THYROID
FUNCTION TESTS
& ADRENAL
FUNCTION TESTS

2. •Thyroid function tests (TFTs)
•The term ‘thyroid function tests‘ refers to the
followinginvestigations:
•TSH (0.4 –4 mU/L)
•Free T4 (9 –25 pmol/L)
•Free T3 (3.5 –7.8 nmol/L)
•There are separate reference ranges for children and
pregnant women.

3. • Hypothyroidism
• Primary hypothyroidism
• Primary hypothyroidisminvolves reduced secretion of thyroid hormone from the thyroid gland itself.
• Pathology which decreases the thyroid’s ability to release T4 and T3 or respond to TSH can, therefore, cause primary hypothyroidism.
• Primary hypothyroidism is themostcommoncause ofhypothyroidism, accounting for 99% of all cases.
• Pathophysiology
• 1.Less T4 and T3 are produced due to the thyroid’s reduced capacity to produce hormone or respond to TSH.
• 2.As a result, there is reduced negative feedback on the pituitary and hypothalamus.
• 3.The reduction in negative feedback results in increased production of TRH (which we don’t typically measure) and TSH.
• 4.The end result is low T4 and T3 and a raised TSH.
• Diagnosis
• The typical findings that would indicate a diagnosis of primary hypothyroidism are as follows:
• Raised TSH:due to the absence of negative feedback.
• Low T4:due to the thyroid’s inability to produce enough T4.
• Anormal T4in the context of araised TSHmay suggestsubclinical hypothyroidism(most commonly caused by underlying autoimmune disease).
• Aetiology

4. •Causes ofprimaryhypothyroidisminclude:
•Autoimmune thyroiditis (50%)
•Iodine deficiency or excess
•Thyroidectomy
•Therapy with radioactive iodine –a treatment for
hyperthyroidism
•External radiotherapy
•Drugs
•Thyroid agenesis or dysgenesis

5. • Secondary hypothyroidism
• Secondary hypothyroidisminvolves a reduction in the hormones that stimulate the thyroid to produce thyroxine.
• Pathology which affects the pituitary and hypothalamic glands can result in decreased production of TRH and TSH, causing secondary hypothyroidism.
• Secondary hypothyroidism is ararecauseofhypothyroidism, accounting for 1% of all cases.
• Pathophysiology
• 1.Decreased production or secretion of TRH and TSH results in decreased stimulation of the thyroid gland.
• 2.The thyroid gland, therefore, produces less T3 and T4.
• 3.The low T3 and T4 would normally stimulate the pituitary and hypothalamic glands to increase TRH and TSH production, however,they are unable to increase production.
• 4.The end result is low T4 and T3 and a normal/low TSH.
• Diagnosis
• The typical findings that would indicate a diagnosis ofsecondaryhypothyroidismare as follows:
• Normal/low TSH:due to a lack of production.
• Low T4:due to the absence of any positive feedback from TSH.
• Aetiology
• Causes ofsecondaryhypothyroidismcan be eitherpituitaryorhypothalamicin origin.
• Pituitary causes:
• Pituitary adenoma: the most common cause.
• Pituitary surgery or radiotherapy which damages the pituitary tissue.
• Hypothalamic causes:
• Hypothalamic or suprasellar tumour.
• Surgery or radiotherapy which damages the hypothalamic tissue.
• TRH is not measured as part of thyroid function tests, as it is only released locally between the hypothalamus and pituitary (soit is not present in representative quantities within the peripheral circulation). Both
structures are commonly grouped together into ‘secondary’ because an issue with TRH gives the same blood test results as an issue with TSH, however, some literature may refer to the hypothalamus as a ‘tertiary’ cause.

6. THYROID
FUNCTION TESTS
& ADRENAL
FUNCTION TESTS

7. •Thyroid function tests (TFTs)
•The term ‘thyroid function tests‘ refers to the
followinginvestigations:
•TSH (0.4 –4 mU/L)
•Free T4 (9 –25 pmol/L)
•Free T3 (3.5 –7.8 nmol/L)
•There are separate reference ranges for children and
pregnant women.

8. • Hypothyroidism
• Primary hypothyroidism
• Primary hypothyroidisminvolves reduced secretion of thyroid hormone from the thyroid gland itself.
• Pathology which decreases the thyroid’s ability to release T4 and T3 or respond to TSH can, therefore, cause primary hypothyroidism.
• Primary hypothyroidism is themostcommoncause ofhypothyroidism, accounting for 99% of all cases.
• Pathophysiology
• 1.Less T4 and T3 are produced due to the thyroid’s reduced capacity to produce hormone or respond to TSH.
• 2.As a result, there is reduced negative feedback on the pituitary and hypothalamus.
• 3.The reduction in negative feedback results in increased production of TRH (which we don’t typically measure) and TSH.
• 4.The end result is low T4 and T3 and a raised TSH.
• Diagnosis
• The typical findings that would indicate a diagnosis of primary hypothyroidism are as follows:
• Raised TSH:due to the absence of negative feedback.
• Low T4:due to the thyroid’s inability to produce enough T4.
• Anormal T4in the context of araised TSHmay suggestsubclinical hypothyroidism(most commonly caused by underlying autoimmune disease).
• Aetiology

9. •Causes ofprimaryhypothyroidisminclude:
•Autoimmune thyroiditis (50%)
•Iodine deficiency or excess
•Thyroidectomy
•Therapy with radioactive iodine –a treatment for
hyperthyroidism
•External radiotherapy
•Drugs
•Thyroid agenesis or dysgenesis

10. • Secondary hypothyroidism
• Secondary hypothyroidisminvolves a reduction in the hormones that stimulate the thyroid to produce thyroxine.
• Pathology which affects the pituitary and hypothalamic glands can result in decreased production of TRH and TSH, causing secondary hypothyroidism.
• Secondary hypothyroidism is ararecauseofhypothyroidism, accounting for 1% of all cases.
• Pathophysiology
• 1.Decreased production or secretion of TRH and TSH results in decreased stimulation of the thyroid gland.
• 2.The thyroid gland, therefore, produces less T3 and T4.
• 3.The low T3 and T4 would normally stimulate the pituitary and hypothalamic glands to increase TRH and TSH production, however,they are unable to increase production.
• 4.The end result is low T4 and T3 and a normal/low TSH.
• Diagnosis
• The typical findings that would indicate a diagnosis ofsecondaryhypothyroidismare as follows:
• Normal/low TSH:due to a lack of production.
• Low T4:due to the absence of any positive feedback from TSH.
• Aetiology
• Causes ofsecondaryhypothyroidismcan be eitherpituitaryorhypothalamicin origin.
• Pituitary causes:
• Pituitary adenoma: the most common cause.
• Pituitary surgery or radiotherapy which damages the pituitary tissue.
• Hypothalamic causes:
• Hypothalamic or suprasellar tumour.
• Surgery or radiotherapy which damages the hypothalamic tissue.
• TRH is not measured as part of thyroid function tests, as it is only released locally between the hypothalamus and pituitary (soit is not present in representative quantities within the peripheral circulation). Both
structures are commonly grouped together into ‘secondary’ because an issue with TRH gives the same blood test results as an issue with TSH, however, some literature may refer to the hypothalamus as a ‘tertiary’ cause.

11. INTRODUCTION
PowerPoint is a very commonly used, fairly
powerful presentation software from Microsoft.
In your academic career (undergrad, graduate,
or professional) there is a good chance that you
have been or will be exposed to this tool.
Furthermore, most of you will need to use it.
This slide show is intended not only to be
presented as a user guide to PowerPoint, but to
be distributed as a way to practice what you
learn as you learn it.