Thyroid Function Tests

Orishaba DianaAnd

Enoch T

Introduction to the Thyroid Gland

• Objectives• Explain the synthesis and regulation of thyroid

hormone production• Describe the actions of thyroid hormones• Describe the etiology, major symptoms and

pathophysiology of hyper and hypothyrodism• Understand the role of thyroid hormone

measurement in the management of thyroid disease

Control of thyroid hormone production

Peripheral tissues

Metabolic Effects of Thyroid Hormones

•Effects on the function of virtually every organ system

•Maintain metabolic stability and increase resting or basal metabolic rate•Increase heart rate•Increase mental alertness•Maintain GI motility & bone turnover•Brain dev’t and skeletal maturation during foetal development

• Thyroid hormones regulate:

- Growth and development

- Temperature

- Oxygen consumption

- Metabolism of carbohydrate, protein and lipid

- TSH secretion

Thyroid disease

• Can be Hypothyroidism or Hyperthyroidism. Either way, this can be a primary disease of the thyroid gland or secondary to brain lesions.

• TFTs alone can differentiate the above.

• Other Ix are important for specific causes eg • Anti-thyroid antibodies (Anti-peroxidase) –in hashimoto’s thyroiditis,

titre tells likelihood of progression to overt hypothyroidism.• TSH receptor antibodies – Grave’s• CT scan in brain lesions• Radio iodine nuclide studies etc

• NB: Goitre refers to thyroid swelling and can be both in patients with hypothyroidism, euthyroidism or hyperthyroidisim.

Primary Causes

• Autoimmune (Hashimoto’s) Thyroiditis

• Congenital hypothyroidism

• Thyroiditis

• Post surgery

• Irradiation (Radioactive iodine, Head & Neck Ca)

• Dietary Iodine deficiency

• Drug effects including anti-thyroid medication

• High amounts of Iodine eg Amiodarone

• Thyroid gland agenesis/dysgenesis

• Infiltrations – Amyloidosis, Haemochromatosis, Fibrous Thyroiditis (Reidel’s)

• Subacute (Viral), Painless (Postpartum) Thyroiditis: Transient Hypothyroidism

HYPOTHYROIDISMLow T3 and/or T4

Other Findings• Anaemia• Hyponatremia• Elevated triglycerides & Cholesterol• Sinus bradycardia• Pericardial effusion• ECG: Low voltage• Slow relaxation of deep tendon

reflexes

Diagnosing Hypothyroidism Insidious onset, so recognition is sometimes

difficult. Always remember the Negative Feedback Loop:

TSH Free T4/T3 Diagnosis

↑ ↓ Overt Primary Hypothyroidism

↑ → (usually low normal)

Subclinical Primary Hypothyroidism

↓ ↓ Secondary Hypothyroidism

Major Causes of Hyperthyroidism

• Graves disease• Toxic multinodular goitre• Toxic nodule• Thyroiditis• Excess replacement • TSH secreting tumour• Amiodarone• Ectopic thyroid tissue

• Trophoblasctic tumours

HYPERTHYROIDISMRaised T3 and/or T4

Other Findings• Increased appetite• Weight loss• Resting tremor• Wide pulse pressure• Flow murmur• Proximal muscle weakness• Brisk deep tendon reflexes

Diagnosing Hyperthyroidism• Try to identify the underlying cause, because

treatments vary• Use Hx, physical exam, Imaging, antibody tests,

etc• Always remember the negative feedback loop

TSH Free T4/T3 Diagnosis

↓ ↑ Overt primary hyperthyroidism

↓ → Subclinical primary hyperthyroidism

↑ ↑ Secondary hyperthyroidism

• TSH (0.3-3.5 mU/L) • Free T4 (10-25 pmol/L)

• Free T3 (3.5-7.5 pmol/L)

Patient A Clinical Biochemistry ------------------------------------------------------------------------------

Sample collected : XX-Aug-XXRef. Range

Serum T.S.H. - - - - - <0.1 mIU/L ( 0.3 – 3.5 ) Free T4 - - - - - 50.2 pmol/L (10.0 -25.0 ) Free T3 - - - - - 22.0 pmol/L ( 3.5 - 7.5 )

1. Patient comes with weight loss and palpitations. Below is his thyroid panel.

What is your specific diagnosis?

Some Questions

Patient A Clinical Biochemistry ------------------------------------------------------------------------------

Sample collected : XX-Aug-XXRef. Range

Serum T.S.H. - - - - - 10.0 mIU/L ( 0.3 – 3.5 ) Free T4 - - - - - 13.2 pmol/L (10.0 -25.0 ) Free T3 - - - - - pmol/L ( 3.5 - 7.5 )

2. Clinical information – Cold intolerance, constipation

What is your specific diagnosis?

Hypothyroidism Treatment

• Depending on the cause but usually is thyroid replacement using Levo thyroxine

Hyperthyroidism Rx

1. Beta Blockers Sympathomimetic blockers Propranolol also inhibits

peripheral conversion of T4 to T3

Sole Tx in transient thyrotoxicosis

2. Antithyroid drugs: Thionamides eg CARBIMAZOLE

Inhibit thyroid hormone synthesis Can induce remission in Grave’s

disease Control thyrotoxicosis before

radioiodine or surgery In Grave’s: Keep on drugs for 12-

24 months, then taper to see if there’s remission

S/Es: Rash, Pruritus, Arthralgias, Agranulocytosis

Pregnancy: Potassium ThioUracil(PTU)

Hyperthyroidism Rx3. RadioActive Iodine

• Oral• Concentrates in the

thyroid gland• Localised destruction• Postablative

hypothyroidism

4. Surgery

• Toxic Adenoma: Lobectomy

• Toxic MNG with compressive symptoms

KI/Lugol’s solution

• Reduces vascularity pre-surgery

Conclusion

Interpretation of TFT’s

TSH T4 T3

Primary hypothyroisism

High low low

Secondary hypothyroidism

low low low

Primary hyperthyroidism

Low high high

Secondary hyperthyroidism

high high high