Endocrinology - thyroid function tests

Question 1

Hyperthyroidism thyroid function tests findings

Answer 1

Primary (thyroid gland problem):

• High T3 and T4
• Low TSH level

Secondary (to pituitary adenoma):

• High T3 and T4
• High TSH level

Question 2

Hypothyroidism thyroid function tests findings

Answer 2

Primary (thyroid gland problem):

• Low T3 and T4
• High TSH level

Secondary (to pituitary adenoma):

• Low T3 and T4
• Low TSH level

Question 3

Antibodies in thyroid disease

Answer 3

Anti-TPO (Antithyroid Peroxidase) Antibodies

• Most relevant autoantibody
• Usually present in Grave’s disease and Hashimoto’s thyroiditis

Antithyroglobulin antibodies

• Usually present in Grave’s Disease, Hashimoto’s Thyroiditis and thyroid cancer
• But can be present in normal individuals

TSH receptor antibodies -autoantibodies that mimic TSH, bind to the TSH receptor and stimulate thyroid hormone release. They are the cause of Grave’s Disease and so will be present in this condition.

Question 4

Imaging in thyroid disease

Answer 4

Thyroid ultrasound
- Useful for diagnosing thyroid nodules

Radioisotope scan

• Used to investigate hyperthyroidism and thyroid cancers
• Radioactive iodine given and taken up by thyroid
• Gamma camera used to detect gamma rays emitted from the radioactive iodine

Question 5

Radioisotope scan findings and meanings

Answer 5

Diffuse high uptake is found in Grave’s Disease

Focal high uptake is found in toxic multinodular goitre and adenomas

“Cold” areas (i.e. abnormally low uptake) can indicate thyroid cancer