As a junior, you will frequently see patients who potentially have thyroid dysfunction. The problem is these patients often present with quite generalised symptoms and you may struggle to know when to send TFTs and what to do when they're abnormal.

Thyroid dysfunction is incredibly common (about 2.5% of the population) with the majority of patients having hypothyroidism. However, as a non-specialist, it is pretty unlikely that you're going to acutely manage thyroid disease without support.

When to send TFTs?
Here are some common reasons you may send TFTs for a patient:
  • Atrial fibrillation
  • Bradycardia or tachycardia
  • Cardiovascular disease (particularly heart failure)
  • Delirium or dementia screen in an elderly patient
  • Lethargy or tiredness
  • Psychosis or confusion
  • Pyrexia of unknown origin
  • Those presenting with other autoimmune conditions (e.g. T1DM, Coeliac)
  • Treatment with amiodarone or lithium
  • Symptoms of hypothyroidism: cold intolerance, lethargy, low mood, constipation, menstrual dysfunction
  • Symptoms of hyperthyroidism: 
    • Sympathetic activity: palpitations, tachycardia, tremor, heat intolerance, anxiety
    • Other: weight loss, menstrual dysfunction, diarrhoea
Thyroid antibodies: Thyroid peroxidase antibody, Thyroglobulin antibody, TSH receptor antibody. The first 2 are tested in hypothyroidism & all 3 in hyperthyroidism.
Thyroid ultrasound: Rarely required

Interpreting TFTs

Disease Free T4 TSH
Hyperthyroidism High Low
Subclinical hyperthyroidism Normal Low
Subclinical hypothyroidism Normal High
Hypothyroidism Low High
Acute illness (non-thyroidal) Low Low

Secondary hypo/hyperthyroidism is pretty rare. The characteristic blood test results would be low T4 & TSH for secondary hypothyroidism & high T4 & TSH for secondary hyperthyroidism. Also, note, we don't routinely measure FT3 but if you do, it usually follows the same pattern as FT4.

Tips when interpreting TFTs
  • Acute non-thyroidal illness or stress (e.g. surgery, starvation, febrile illness) can cause any pattern of abnormal TFTs, but both TSH & T4 being low are most common. This is known as sick euthyroid syndrome. This may occur in as much as 15% of inpatients & usually resolves once the patient is no longer ill or on repeat testing 6-8 weeks after discharge. 
  • Levothyroxine has a 7-day half-life. This means you won't usually have an issue if you miss 1 or 2 tablets
  • In hypothyroidism, the TSH takes a while to correct so acutely the patient may have normal T4 with a low TSH. You need to wait 6-8 weeks before you measure the TFTs after adjusting the dose of levothyroxine
  • In overtreated hypothyroidism, the bloods may look like hyperthyroidism with a low TSH & high T4
  • Normal TFTs in a patient with thyroid nodules/multinodular goitre could be thyroid cancer. Discuss this with your endocrine team
  • The normal range of TFTs varies by hospital & are completely different for pregnancy

Hypothyroidism
Subclinical hypothyroidism warrants repeat TFTs at 3-6 months. If they have thyroid antibodies, there's a 5% annual chance of developing hypothyroidism. If they're antibody negative, it is far lower with testing usually every 3 years. Subclinical hypothyroid patients who are trying to conceive, pregnant, symptomatic or have a goitre may be treated.

99% is primary with chronic autoimmune (Hashimoto's) being most common in the UK. Hypothyroidism may also occur following radioiodine therapy for hyperthyroidism. Levothyroxine is the treatment - 50mcg starting dose but 25mcg for the elderly or those with ischaemic heart disease. Severe hypothyroidism (myxoedema coma) can be life-threatening with hypothermia, hypoglycaemia & hyperventilation

Hyperthyroidism
Subclinical hyperthyroidism warrants repeat TFTs at 4-8 weeks. It is important to look for drug causes.
99% is primary hyperthyroidism with Graves disease being most common. Look for a tender or nodular goitre clinically which might suggest it isn't Graves disease. 

Graves disease:
  • Anti-TSH antibodies are positive in about 80% and eye signs can also occur
  • It tends to burn out after 18 months of treatment, but in about 30% it will relapse
  • For hyperthyroidism, propranolol is used for the awful sympathetic overdrive symptoms
  • Do note that Carbimazole can cause a rash & agranulocytosis
  • T3 is useful as about 5% of patients have an isolated T3 thyrotoxicosis with a normal FT4

Thyroid Storm
This is pretty rare but is an extreme state of thyrotoxicosis with profuse sweating, agitation, fever & tachycardia. Here is a calculator to quantify the likelihood of a patient having a thyroid storm. It can occur with thyroidectomy, trauma, childbirth, infection, untreated hyperthyroidism, radioactive iodine treatment, DKA. Call the medical registrar urgently for ABCDE & anti-thyroid therapies

Thyroid Masses or Tenderness
Usually referred to the ENT or general surgery team. In addition to features of thyroid dysfunction, look for dysphonia & compression symptoms (dysphagia, orthopnoea or stridor). Examine for Pemberton's sign (raising arms for 60 seconds to look for a purple face in SVC obstruction)

Differentials Features Management
Subacute (de Quervain's) thyroiditis Very painful enlarged thyroid with transient hyperthyroidism followed by hypothyroidism NSAIDs (usually self limiting)
Acute Suppurative Thyroiditis Thyroid abscess due to infected haemorrhagic cyst, subacute thyroiditis or post op (FNA/hemithyroidectomy)
An infected thyroglossal duct cyst will rise on sticking the tongue out.
Antibiotics. Sometimes drainage but discuss with seniors
Goitre Beware of goitres causing compressive symptoms - particularly compressing the airway Urgently escalate airway concerns
Haemorrhagic cyst Enlarging solitary nodule that's clinically tender with normal inflammatory markers Discuss with registrar in case urgent action required
Thyroid malignancy Acute presentation is rare but classic enlarging mass & constitutional symptoms Discuss with registrar as urgent action may be required due to compression

References & Further Reading
Written by Mr Tobias James (ST2 ENT) & Dr Akash Doshi (ST3 Endocrinology)