T4 Free, Direct


For: ,

Quest Diagnostics Test Code: 866

T4 Free test is done for diagnosis of hypothyroidism and hyperthyroidism.

T4, also known as thyroxine, is a hormone that is released from the thyroid gland. Together with the hormone T3, they help to regulate body metabolism and energy expenditure rate. T4 is released into the bloodstream from the thyroid gland and travels to its target organs while being bound to plasma proteins. When T4 is bound to plasma proteins, it is in its inactive form. If it is not bound, it is referred to as free T4, and this is the active hormone which can exert its effect. Free T4 is an easy test to perform as a marker of thyroid function, for disease like hyper and hypothyroidism, and this the most commonly used test, along with TSH, for thyroid function in the clinical setting.

This test is performed in following conditions such as:

Signs and symptoms of hyperthyroidism
• Weight loss
• Increased heart rate
• Anxiety
• Difficulty sleeping
Signs and symptoms of hypothyroidism
• Weight gain
• Dry skin
• Constipation
• Cold intolerance

Also Known As: Free T4, Free Thyroxine


Specimen Collected
  • Blood
Estimated Time Taken

Turnaround time for a Free T4 test is typically 1 business day.