A doctor diagnoses mild, or subclinical, hypothyroidism through a medical history and physical exam. If your doctor suspects that you have subclinical hypothyroidism, you will have lab tests to confirm the diagnosis.

Subclinical hypothyroidism is diagnosed when you have:

• No symptoms or mild symptoms of hypothyroidism. Examples are fatigue, cold intolerance, consistent weight gain, depression, or memory problems.
• A mildly high thyroid-stimulating hormone (TSH) level.
• A normal thyroxine (T4) level.

Some people with subclinical hypothyroidism may test positive for antithyroid antibodies. These point to Hashimoto's thyroiditis, which may cause a gradual loss of thyroid gland function.

Research does not provide clear evidence to support treatment of every person who has subclinical hypothyroidism. And many doctors disagree whether it should be treated. When making the decision to treat subclinical hypothyroidism, you and your doctor will talk about the benefits of treatment compared to the cost of medicine and monitoring symptoms. Some studies have shown that treatment of subclinical hypothyroidism may lower cholesterol levels. But more research is needed.