A TSH level of 0.65 indicates a thyroid that is functioning well. Normal TSH levels range between 0.4 and 4.0 milli-international units per liter, MedlinePlus says.
Doctors measure the level of thyroid-stimulating hormone to detect whether the thyroid is working sufficiently. Patients undergo a simple blood test, and they do not need to fast before it. Doctors typically order the test when patients show signs of an underactive or overactive thyroid. Hypothyroidism, the condition that indicates an underactive thyroid, has symptoms such as weight gain, depression, fatigue and intolerance to cold. People with an overactive thyroid, or hyperthyroidism, experience weight loss, nervousness, sleep problems and an increased appetite, MedlinePlus says.
Patients with hyperthyroidism may be cured, but most with hypothyroidism take thyroid medications for the rest of their lives. In some cases, doctors may remove the thyroid, and patients need to keep taking medications in order to supplement the lack of thyroid hormone, MedlinePlus asserts.
People who have a TSH level of 0.65 milli-international units per liter, however, likely have a normally functioning thyroid because the number falls inside the ideal range, MedlinePlus says. If they have symptoms of a malfunctioning thyroid but receive a normal reading, doctors can redo the test or examine other causes for the symptoms.