T4 (Thyroxine)

Thyroxine (T4) is the main hormone produced by the thyroid gland and acts as the body's metabolic thermostat, influencing how quickly cells use energy. This test measures the total amount of T4 circulating in your bloodstream and is typically requested when thyroid function is in question, whether you are experiencing symptoms of an underactive or overactive thyroid, or you are already on thyroid medication and need your levels monitored. It is also a routine part of a broader thyroid assessment and can be useful when investigating fatigue, unexplained weight change, mood disturbance, or menstrual irregularities.

The analysis is performed on a simple blood sample using a validated immunoassay technique, delivering a reliable measurement of your circulating thyroxine level.

Hormones
- Thyroxine (T4)

Why it matters
Thyroxine is central to regulating metabolism, heart rate, body temperature, and energy levels. An abnormal T4 result can point towards an underactive thyroid (hypothyroidism), an overactive thyroid (hyperthyroidism), or signal the need for further testing such as TSH and free T4. Identifying a T4 imbalance early allows you and your doctor to take timely action, whether that means starting treatment, adjusting an existing dose, or investigating other underlying causes of your symptoms.