Thyroid

Question 1

What tests can be used to investigate suspected thyroid disease?

Answer 1

Total T4 and T3

Free T4 and T3

Thyroid stimulating hormone

Thyroid peroxidase antibodies

TSH receptor antibodies

Question 2

How does pregnancy affect thyroxine levels in the blood?

Answer 2

Pregnancy raises levels of thyroid binding globulin.

This increases the amount of thyroxine bound and reduces the amount of free thyroxine, thereby reducing the inhibition of the pituitary by thyroxine. This causes an increase in TSH production, and an increase in thyroxine production.

Question 3

How does the oral contraceptive pill affect thyroxine levels in the blood?

Answer 3

The oral contraceptive pill raises levels of thyroid binding globulin.

This increases the amount of thyroxine bound and reduces the amount of free thyroxine, thereby reducing the inhibition of the pituitary by thyroxine. This causes an increase in TSH production, and an increase in thyroxine production.

Question 4

Which drugs can affect tests for thyronines?

Answer 4

Amiodarone

It contains a lot of iodine and may affect the results of thyronine tests.

Lithium

Interferon

Rifampicin

Oral contraceptive pills

Question 5

How do you diagnose hypothyroidism?

Answer 5

1. Serum Free T4 is below reference range
2. Serum TSH is greater than 10 mU/L

(Reference range is different for pregnancy between the various trimesters)

3. Thyroid peroxidase antibody assay - If Hashimoto’s thyroiditis is suspected
4. FBC - associated anemia
5. HbA1C - associated T1 DM
6. Serum lipids - associated hypercholesterolaemia

Question 6

Under what circumstances do you perform a USS of the thyroid?

Answer 6

Goitre presence.

Hypothyroidism and hyperthyroidism are not reason to perform a USS.

Question 7

How do you diagnose hyperthyroidism?

Answer 7

1. Serum TSH is less than 0.5 mU/L
2. Serum free T4 will be raised
3. TPO antibody assay

Question 8

What is the investigation pathway for a goitre?

Answer 8

1. Thyroid exam
2. Serum TSH measurement
3. Serum free T4 measurement
4. USS neck
5. Needle biopsy of goitre (rule out cancer)

Biopsy results:
THY 1 - poor specimen 
THY 2 - benign
THY3 - indeterminate (adenoma or carcinoma)
THY 4 - suspicious
THY 5 - diagnostic of malignancy