Depression: Low thyroid function reduces the effect of serotonin in the brain, and reduced serotonin can lead to depression. Correcting underlying thyroid imbalance may improve or, in some cases, even eliminate symptoms of depression.

Fatigue: Severe tiredness and exhaustion can be symptoms of low thyroid function. These may also be signs of poor adrenal function, so talk with your health care provider to decide whether a thyroid test or an adrenal function test is best for you.

Coldness: Because thyroid hormone is needed to get the body's "furnace' working, low thyroid function often results in low body temperature. In fact, monitoring body temperature is another way to assess thyroid function. Patients with consistently cold hands and feet may have a poorly functioning thyroid.

Arthritis and Muscle Cramps: Low levels of thyroid hormone can cause deposits to form in joints and tissues. Most cases of joint pain related to hypothyroidism involve knees and hands. Muscle cramps can occur in almost any muscle.

Headaches: The headaches associated with hypothyroidism tend to be mild but continuous, and often affect both sides of the head. It is not known why people with low thyroid function are more prone to headaches.

Weight Gain: A lack of thyroid hormone can cause weight gain, even though appetite may decrease. The weight gain occurs because there is insufficient thyroid hormone to regulate protein, fat and carbohydrate metabolism.

• TSH (thyroid stimulating hormone) is a hormone secreted in the brain to control thyroid function. A blood test for TSH is still considered the "gold standard' test for diagnosing thyroid disease however, many women and men have normal serum TSH levels despite having classic symptoms of low thyroid function. The urinary thyroid assessment offers an alternate means of measuring thyroid function when the patient is symptomatic but conventional serum tests are normal.

• If heavy metal toxicity or high levels of cortisol are present, TSH levels in serum may be normal, even if thyroid function is poor.

• Patients who are taking thyroid hormones (e.g. Synthroid or Eltroxin), may experience low thyroid symptoms even though serum TSH is normal. This is because the serum TSH frequently fails to reflect how well supplemented thyroid hormone is being delivered to tissue.