TSH and T4 levels determine thyroid gland function. The pituitary gland secretes TSH, which affects the thyroid's release of T4. High or low levels of TSH and T4 usually signal thyroid disease or abnormal thyroid function. High levels of TSH suggest hypothyroidism, a condition where the thyroid is under-active and does not produce enough T4 or other thyroid hormones. A normal TSH range is from 0.3 to 5.0, and a normal T4 level is 4.5 to 11.2. However, these may vary from lab to lab. Weight gain, a feeling of constant fatigue, and/or depression are common signs that TSH or T4 levels are out of whack. If left untreated, hypothyroidism can lead to obesity, joint pain, infertility, and heart disease.
TSH, also called thyrotropin, is a thyroid-stimulating hormone. TSH is created and secreted by the pituitary gland and is responsible for regulating the hormonal (endocrine) function of the thyroid gland. More specifically, TSH causes the thyroid to release thyroxine (T4) and triiodothyronine (T3), other hormones necessary for bodily function.
According to the American Association of Clinical Endocrinologists (AACE), a normal TSH range is from 0.3 to 5.0. However, AACE strongly encourages doctors to treat and further test patients with a TSH level higher than 3.0, as anything higher may be an early sign of future thyroid underactivity and/or a mild case of underactivity.
Thyroxine, or T4, is the main hormone secreted by the thyroid and plays a part in physical development. T4 also affects the rate of metabolic processes in the body. More specifically, the amount of T4 in the human bloodstream affects the release of TSH by the pituitary gland, which subsequently affects thyroid function. For example, if levels of T4 are low, the pituitary gland will increase production of TSH, which will then stimulate the thyroid into secreting more T4. Conversely, if T4 levels are high, the pituitary gland will decrease TSH production.
Realizing that specific values range between each lab, on average, a typical normal range for T4 levels is 4.5 to 11.2 micrograms per deciliter (mcg/dL), according to MedlinePlus Medical Encyclopedia.
Hypothyroidism, also called an underactive thyroid, is a medical condition where the thyroid gland does not synthesize and secrete enough T3 and T4 thyroid hormones. If tests show that TSH levels are high, the patient is typically diagnosed with hypothyroidism.
Hypothyroidism is typically asymptomatic, particularly in the early stages. However, individuals with hypothyroidism or abnormal TSH and T4 levels may feel fatigued, depressed, sluggish, or weak. Other symptoms include increased sensitivity to cold, constipation, pale skin, dry skin, puffy face, hoarse voice, hypertension, weight gain, heavy periods, and brittle nails.
Treatment for hypothyroidism and abnormal TSH and T4 levels includes regular prescription medication (typically synthesized hormones).