Test Details: T4 is the main hormone formed by the thyroid gland. Most T4 is bound to proteins, while a small portion is unbound. A total T4 test measures free and bound T4 together. T4 testing is ordered in case of abnormal TSH result, hyperthyroidism, hypothyroidism, patient on replacement therapy, new-born screening. 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.