Test Details: T4 is the main hormone formed by the thyroid gland. Most T4 is bound to proteins, while a small portion is unbound. Free T4 measures thyroid hormone that is not bound and is able to enter and affect the body tissues. Free T4 evaluation accurately gives information regarding thyroid gland functional status. T4 testing is ordered in case of abnormal TSH result, hyperthyroidism, hypothyroidism, patient on replacement therapy, new-born screening and various other conditions. Symptoms of thyroid disorder include fatigue, weight gain or loss, feeling hot or cold, dry skin, thin or dry hair, constipation or diarrhoea, irregular menstrual periods, etc.