Hypothyroidism occurs when your thyroid gland underproduces thyroid hormones, which are necessary for the regulation of many body functions crucial to health.
Signs and symptoms of hypothyroidism may include fatigue and weakness, a slow heart rate, increased sensitivity to cold, dry skin and hair, constipation, unexplained weight gain, or muscle aches. However, these signs and symptoms aren't thyroid specific and could be due to other causes.
Diagnosis of hypothyroidism is through blood tests that measure the thyroid-stimulating hormone (TSH) and the thyroid hormones thyroxine (T4) and triiodothyronine (T3). In most cases of hypothyroidism associated with symptoms related to thyroid hormone levels, the TSH is quite elevated, along with low T4 and T3 levels.
However, it's not always so straightforward. Subclinical hypothyroidism is a category of hypothyroidism in which only the TSH test results are slightly abnormal. Generally, in this category, the TSH level is in the range of 5 to 10 milliunits per liter (mU/L). There are often no symptoms, or symptoms are mild or vague enough to be attributable to other things.
A long-debated question is whether subclinical hypothyroidism should be treated with replacement synthetic thyroid hormones. According to a 2018 review of research published in the journal JAMA, treating people with a TSH level at or below 10 mU/L isn't effective. It's often not associated with improvements in quality of life — or of improvement in signs and symptoms, which may include depression, fatigue or tiredness, strength loss, cognitive decline, or weight gain.
Mayo Clinic thyroid experts generally agree with this...
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