Imperial Collage Healthcare

Free T4 (free thyroxine)


Test Background
Thyroid disorders are common medical conditions, more common in women than men and increasing with age in both sexes. Thyroxine circulates bound to thyroxine binding globulin (TBG) and albumin, and the free fraction represents the biologically active fraction. Free T4 is measured and, together with TSH, is a frontline test for investigation and monitoring of thyroid disorders.


Clinical Indications

  • Signs and symptoms of hypothyroidism include: poor muscle tone (muscle hypotonia), fatigue, increased sensitivity to cold, constipation, depression, muscle cramps and joint pain, carpal tunnel syndrome, goiter, paleness, osteoporosis, dry/itchy skin, weight gain and water retention, bradycardia and abnormal menstrual cycles
  • Signs and symptoms of hyperthyroidism include: weight loss (often accompanied by an increased appetite), anxiety, hair loss, muscle aches, weakness, fatigue, hyperactivity, irritability, hypoglycemia, apathy, polyuria, polydipsia, delirium, tremor, myxoedema and sweating. Additionally: palpitations and arrhythmias (notably atrial fibrillation), shortness of breath (dyspnea), nausea, vomiting, and diarrhoea
  • Differential diagnosis of: hyperlipidaemia, osteoporosis and sub-fertility
  • Screening following post-partum thyroiditis or in Down’s and Turner’s syndromes
  • Amiodarone and lithium therapy
  • Monitoring established thyroid disease


Reference Range

9-23 pmol/L


Sample Required
SST (gold top)


Sample Volume
0.5 mL


Turnaround Time
1 day


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