Investigations

Question 1

What would be the results of thyroid function tests in primary hyperthyroidism?

Answer 1

Elevated free T4 + T3, suppressed TSH

Production of TSH is regulated by feedback from circulating free thyroid hormone concentrations.

Question 2

What are the thyroid function tests?

Answer 2

• Total T4: 50-150nmol/l
• Free T4: 10-25pmol/l
• Total T3
• Free T3: 1.1-3.0 nmol/l
• TSH - immunoassay: 0.2-3.0mU/L
• Antibodies: TPO Abs (when exposed to circulation) + TSH-R Abs (on surface of follicular cells)

Question 3

What do T4, T3 and TSH show?

Answer 3

• Overactive thyroid: high T4 + T3, low TSH

- Underactive thyroid: low T4, high TSH

Question 4

What other factors raise TBG?

Answer 4

• Pregnancy
• OCP/HRT
• Hepatitis
• Amiodarone can increase iodine concentration > toxic to thyroid

Question 5

What the TFT’s show in primary and secondary hypothyroidism?

Answer 5

• Primary: low T4, low T3, high TSH

- Secondary: low T4, low T3, low/normal TSH

Question 6

What the TFT’s show in primary and secondary hyperthyroidism?

Answer 6

• Primary: high T4, high T3, low TSH

- Secondary: high T4, high T3, high TSH

Question 7

Why is TSH a critical test in hypothyroidism?

Answer 7

• TSH > 2mU/L increases risk of developing hypothyroidism in next 2 years
• Positive TPO Abs increases risk further

Question 8

How do you assess a goitre?

Answer 8

• Assess thyroid status (toxic, hypo, euthyroid)
• Are there compression symptoms e.g. oesophagus, trachea
• Multinodular i.e. thyrotoxicosis
• Diffuse: graves disease, hypothyroidism, colloid goitre (euthyroid), iodine deficiency, drugs (lithium etc)

Question 9

How to evaluate thyroid nodules?

Answer 9

• Frequent benign disease, low risk of malignancy
• Ultrasound
• Fine needle aspiration

Question 10

What is the diagnostic approach for thyroid nodules?

Answer 10

• Benign: Thy2 - usually colloid nodules (70%)
• Indeterminant: Thy3 - follicular lesion (10-20%)
• Suspicious of malignancy: Thy4 - 30% malignant
• Diagnostic of malignancy: Thy5 - clear features of papillary, follicular, medullary or other carcinoma, lymphoma, metastasis

Question 11

What factors decrease TBG?

Answer 11

• Nephrotic syndrome
• Malnutrition
• Drugs (androgens, corticosteroids, phenytoin)
• Chronic liver disease
• Acromegaly

Question 12

What other tests are used for thyroid disease?

Answer 12

• Thyroid antibodies: antithyroid peroxidase (TPO) antibodies may be increased in autoimmune thyroid disease > leading to increased risk of problems
• TSH receptor antibody: may be increased in Graves disease
• Serum thyroglobulin
• Ultrasound
• Isotope scan

Question 13

Who should you screen for abnormalities in thyroid function?

Answer 13

• AF
• Hyperlipidaemia
• Diabetes mellitus - annual review
• T1DM in 1st trimester and post-delivery
• Amiodarone or lithium (6 monthly)
• Down’s or Turner’s syndrome or Addison’s disease (annually)

Question 14

What would be the results of a radioactive iodine uptake scan for graves disease and post-partum thyroiditis?

Answer 14

GD: normal or increased
PPT: decreased