Diagnosis of hypothyroidism is based on a person's medical history, a physical examination, and blood tests.
If a physician suspects hypothyroidism, he or she will look particularly at the cardiovascular system, the skin, hair, eyes, reflexes, and body temperature. The physical exam also may reveal an enlarged thyroid, which is called a goiter.
In Hashimoto's thyroiditis, if a goiter is present, it will not be tender and will have a rubbery feel.
If the goiter is tender, the cause may be subacute thyroiditis, an inflammation of the thyroid that often follows an upper respiratory infection.
Blood tests check the levels of the thyroid hormones T4, T3, and TSH, among other related substances.
Abnormally low levels of T4 and T3 indicate hypothyroidism is present.
The TSH (thyroid-stimulating hormone) level is especially important in determining whether the condition is due to a problem in the thyroid gland or in the part of the brain that stimulates thyroid function.
If the TSH level in the blood is high, the abnormality is within the thyroid gland. A high TSH level suggests that the thyroid gland is not responding properly to the stimulating effect of the TSH on the thyroid gland.
If the TSH level in the blood is low, the abnormality is within the brain or pituitary gland in the brain. It suggests that the pituitary is not releasing adequate amounts of TSH to stimulate the thyroid gland, despite levels of thyroid hormone low enough that it should do so.
Among adults with hypothyroidism, roughly 95% of cases represent problems in the thyroid gland. In about 5% of cases, the abnormality is found in the brain or in the pituitary gland, almost always the pituitary gland.
If blood tests suggest that the problem is in the glands in the brain, imaging tests of the brain may be necessary. These include CT scans, which are sophisticated x-rays, and MRI scans, which use magnets to create images of the inner body.
Other blood tests include an antibody test, which is a blood test to detect antithyroid antibodies. High levels of these antibodies suggest that a person may have Hashimoto's thyroiditis.
Need To Know:
Of the blood tests for hypothyroidism, the TSH is the most sensitive test. The role of TSH is to stimulate the thyroid gland to produce thyroid hormone when the level of hormone in the body drops.
If the TSH level is above 6, then a diagnosis of hypothyroidism will be made.
However, if the thyroid hormone levels are normal and the person has no symptoms, then the conditions is said to be "subclinical." This means that the hypothyroidism has been diagnosed by a blood test only, since there are no symptoms.
Most people feel best when their TSH level is between 0.5 and 2.5.
Nice To Know:
The American Thyroid Association, a national professional organization of thyroid specialists, recommends that women over age 35 should be screened every five years for hypothyroidism.