TSH is a very sensitive indicator of the functional status of the thyroid gland. If the TSH level is elevated, the patient is in a state of hypothyroidism. If the TSH level alone is high and the free thyroxine level is normal, this is called subclinical hypothyroidism. At this time, the thyroid hormone level has not started to decline, but because the TSH is sensitive, it has responded, suggesting that the body is starting to develop an early state of hypothyroidism. If the TSH is high and is accompanied by a decrease in free thyroid hormone levels, you have entered the clinical phase of hypothyroidism. The treatment of subclinical and clinical hypothyroidism is different. Subclinical hypothyroidism does not require replacement therapy, while clinical hypothyroidism requires oral eugenol replacement therapy.